<P> The season was ordered in January 2017, and filming began that July . Grant Gustin stars as Barry, with principal cast members Candice Patton, Danielle Panabaker, Carlos Valdes, Keiynan Lonsdale, Tom Cavanagh, and Jesse L. Martin also returning from previous seasons, and are joined by Neil Sandilands . </P> <P> The fourth season began airing on October 10, 2017, and ran for 23 episodes on The CW until May 22, 2018 . </P> <Table> <Tr> <Th> No . overall </Th> <Th> No. in season </Th> <Th> Title </Th> <Th> Directed by </Th> <Th> Written by </Th> <Th> Original air date </Th> <Th> Prod . code </Th> <Th> U.S. viewers (millions) </Th> </Tr> <Tr> <Th> 70 </Th> <Td> </Td> <Td> "The Flash Reborn" </Td> <Td> Glen Winter </Td> <Td> Story by: Andrew Kreisberg Teleplay by: Todd Helbing & Eric Wallace </Td> <Td> October 10, 2017 (2017 - 10 - 10) </Td> <Td> T27. 13401 </Td> <Td> 2.84 </Td> </Tr> <Tr> <Td_colspan="8"> Iris has been aiding Team Flash in Central City for six months, but refuses to grieve Barry . A flying samurai with superpowers appears in Central City, threatening to destroy the city if the real Flash does not face him . Cisco reveals he has formulated a way to bring back Barry without destabilizing the Speed Force and tracks down Caitlin for help, but is forbidden by Iris to bring Barry back . Against Iris' orders, Team Flash successfully returns Barry, who rambles random statements and continually writes symbols on the walls . Wally engages the samurai, but is defeated . Cisco deciphers Barry's writings and finds an apparently meaningless sentence . In an attempt to recover Barry's memories, Iris gives herself up to the samurai . The plan works and Barry speeds away, rescuing Iris and defeating the samurai, who is revealed to be an android . Caitlin rejoins Team Flash, but is revealed to have been working for a mobster called Amunet, while also continuing to prevent the Killer Frost personality from emerging . The "Samuroid" is revealed to have been controlled by a supremely intelligent man in a superpowered wheelchair, whose plan was to draw out the Flash for his next schemes . </Td> </Tr> <Tr> <Th> 71 </Th> <Td> </Td> <Td> "Mixed Signals" </Td> <Td> Alexandra La Roche </Td> <Td> Jonathan Butler & Gabriel Garza </Td> <Td> October 17, 2017 (2017 - 10 - 17) </Td> <Td> T27. 13402 </Td> <Td> 2.54 </Td> </Tr> <Tr> <Td_colspan="8"> When Barry, Joe, and Cisco report to a crime scene, they discover remnants of a mysterious code . Cisco presents Barry with a technologically advanced suit, intended to facilitate his activities . He tests it out, trying to save someone from a haywire car controlled by metahuman Ramsey Deacon . Gypsy arrives on Earth - 1 for a date with Cisco, who is forced to cancel it so as to focus on Deacon . Acting on a suggestion from Caitlin, Iris signs her and Barry up for couples therapy to sort out their relationship . Deacon kidnaps a witness, a former member of a tech team that stole his idea for profit . Barry and Wally go to save him, but Deacon uses his abilities to send Barry's suit haywire . On Iris' instruction, Barry throws lightning at himself, shorting out his suit . He then incapacitates Deacon, who is locked up in the meta wing of Iron Heights, revealed to be part of the Thinker's plan . Cisco finally goes out with Gypsy . Wondering how Deacon gained his powers being absent during the particle accelerator incident, Barry and Joe learn from Deacon that there are "others ." </Td> </Tr> <Tr> <Th> 72 </Th> <Td> </Td> <Td> "Luck Be a Lady" </Td> <Td> Armen V. Kevorkian </Td> <Td> Sam Chalsen & Judalina Neira </Td> <Td> October 24, 2017 (2017 - 10 - 24) </Td> <Td> T27. 13403 </Td> <Td> 2.62 </Td> </Tr> <Tr> <Td_colspan="8"> In flashbacks, the Thinker observes Becky Sharpe, a woman with seemingly unending bad luck, and determines that she will be easily manipulated . In the present, Becky robs a bank and gets away when Barry slips on marbles . Harry arrives from Earth - 2 and tells Wally that Jesse has decided to break up with him in order to focus on her vigilantism . Cisco deduces that Becky is a metahuman with the power of favorable luck while inducing misfortune to others . Barry realizes that the portal he used to escape the Speed Force exposed an entire busload of people, including Becky and Deacon, to transformative dark matter . Harry informs Cisco that Jesse has expelled him from her crime - fighting team due to his attitude . Becky's powers expand out of control, reactivating the particle accelerator, which Harry deliberately allows, nullifying Becky's powers and leading to her incarceration . Cisco and Harry identify twelve new metahumans created on the bus and the latter suspects that an unknown party has manipulated the events surrounding Barry's return . Wally decides to leave on a journey to find himself . The Thinker is revealed to be spying on S.T.A.R. Labs through the "Samuroid" helmet . Joe learns Cecile is pregnant . </Td> </Tr> <Tr> <Th> 73 </Th> <Td> </Td> <Td> "Elongated Journey Into Night" </Td> <Td> Tom Cavanagh </Td> <Td> Sterling Gates & Thomas Pound </Td> <Td> October 31, 2017 (2017 - 10 - 31) </Td> <Td> T27. 13404 </Td> <Td> 1.99 </Td> </Tr> <Tr> <Td_colspan="8"> Gypsy's father, Breacher, attacks Cisco, vowing to hunt and kill him in 24 hours, allowing the romance should he survive . Team Flash learns that the bus driver was murdered and tracks down another passenger, Ralph Dibny, former corrupt CCPD detective exposed by Barry and currently an infamous private investigator . As two thugs attack Dibny, he is revealed to have the power to stretch . Caitlin stabilizes his powers with a serum . The team learns that Ralph has been blackmailing Mayor Bellows for adultery, with the latter revealed to have hired the thugs . Barry confronts Ralph for his actions while the latter scolds him, claiming to have been a "good cop". He later stops blackmailing Bellows, who still attempts to kill him while Breacher mistakes the former for a Plastoid, the species that invaded Earth - 19 previously, and attacks him . Cisco intervenes and saves Ralph, whom Barry, having revealed his alter - ego, convinces to help arrest an escaping Bellows . Admiring Cisco's gallantry, Breacher allows the relationship . Barry recruits Ralph for Team Flash and learns that someone named DeVoe instructed Ralph to watch Bellows . Barry remembers that both Abra Kadabra and Savitar mentioned DeVoe . Meanwhile, Caitlin finds a message on her apartment door . </Td> </Tr> <Tr> <Th> 74 </Th> <Td> 5 </Td> <Td> "Girls Night Out" </Td> <Td> Laura Belsey </Td> <Td> Lauren Certo & Kristen Kim </Td> <Td> November 7, 2017 (2017 - 11 - 07) </Td> <Td> T27. 13405 </Td> <Td> 2.38 </Td> </Tr> <Tr> <Td_colspan="8"> While failing to track DeVoe, Team Flash is visited by Felicity, who joins Iris's bachelorette party . Mocking Cisco's plans for Barry's bachelor party, Ralph takes the men to a strip club, where they learn that Cecile's daughter, Joanie, is working . Joe confronts her, who states she is only doing feminist research . Ralph incites a brawl, leading to the men's arrest until Harry posts bail . Meanwhile, Amunet's enforcer, Norvock, demands Caitlin's return and attacks the women when she refuses . Killer Frost emerges and repels him, later telling Iris that Caitlin accepted Amunet's employment in exchange for the means to control Frost . Learning that Amunet is holding a metahuman she calls the "Weeper", whose tears are a strong narcotic, prisoner and intends to sell him, Iris's party decides to stop her . Though Caitlin refuses to join, she attacks Amunet when seeing her friends in danger . Using a strong magnet, the team robs Amunet's metal shards, leaving her powerless . Iris dissuades Frost from killing Amunet, who promises revenge . Both parties refuse to tell each other about their adventures . Iris asks Caitlin to be her maid of honor while Joe convinces Joanie to tell Cecile about her research . DeVoe captures the Weeper . </Td> </Tr> <Tr> <Th> 75 </Th> <Td> 6 </Td> <Td> "When Harry Met Harry ..." </Td> <Td> Brent Crowell </Td> <Td> Jonathan Butler & Gabriel Garza </Td> <Td> November 14, 2017 (2017 - 11 - 14) </Td> <Td> T27. 13406 </Td> <Td> 2.46 </Td> </Tr> <Tr> <Td_colspan="8"> Barry trains Ralph to use his abilities, with Cisco making a stretchable suit for him . Another bus metahuman, a Lakota Sioux Native named Mina Chayton, who can animate statues, starts attacking Central City & stealing pieces of a Black Bison necklace, which she claims belongs to her tribe . When Barry and Ralph catch up to her, she attacks Barry with a caveman statue and attempts a getaway . Ralph chooses to stop her, but a little girl is injured in the process . Ralph regrets his actions, but is comforted by Barry . Chayton escapes CCPD, going after the last necklace piece held at the museum . When Barry and Ralph confront her, she brings a dinosaur skeleton to life . Barry arrests Chayton while Ralph saves a security guard from the skeleton . Later, Ralph reveals he mailed the necklace back to Chayton's tribe, before visiting the little girl in the hospital, using his abilities to entertain her . Meanwhile, Harry, trying to make friends, works with his doppelgangers of alternate Earths, The Council of Wells . They figure out that DeVoe is a man named Clifford DeVoe . Barry and Joe head to DeVoe's house, to find out that he is a middle - aged man in a wheelchair . </Td> </Tr> <Tr> <Th> 76 </Th> <Td> 7 </Td> <Td> "Therefore I Am" </Td> <Td> David McWhirter </Td> <Td> Eric Wallace & Thomas Pound </Td> <Td> November 21, 2017 (2017 - 11 - 21) </Td> <Td> T27. 13407 </Td> <Td> 2.20 </Td> </Tr> <Tr> <Td_colspan="8"> Barry and Joe interrogate DeVoe and his wife to try and get more information . In flashbacks, DeVoe and his wife build a thinking cap to improve his brain capacity, powering it through the particle accelerator explosion . DeVoe's increased brain power accelerates his amyotrophic lateral sclerosis, forcing his wife to build him a special chair to keep him alive . Barry discovers the camera in the Samuroid head and goes to DeVoe's house, narrowly avoiding being caught by DeVoe's wife . Barry later confronts DeVoe, who reveals his true identity, leading to Cisco dubbing him "The Thinker". Wally returns to Team Flash from Blue Valley . </Td> </Tr> <Tr> <Th> 77 </Th> <Td> 8 </Td> <Td> "Crisis on Earth - X, Part 3" </Td> <Td> Dermott Downs </Td> <Td> Story by: Andrew Kreisberg & Marc Guggenheim Teleplay by: Todd Helbing </Td> <Td> November 28, 2017 (2017 - 11 - 28) </Td> <Td> T27. 13408 </Td> <Td> 2.82 </Td> </Tr> <Tr> <Td_colspan="8"> <P> Barry, Oliver, Sara, Alex, Martin and Jax wake up in a Nazi concentration camp on Earth - X wearing power dampeners . The arriving SS Sturmbannführer is revealed to be the Earth - X doppelgänger of Quentin Lance, who plans to execute them, but they are saved by Citizen Cold (the Earth - X doppelgänger of Leonard Snart) and Ray Terrill . Snart and Terrill take them to the headquarters of the Freedom Fighters, where the team meets the resistance movement's leader, General Schott (Winn Schott's Earth - X doppelgänger). They learn that the only way back to Earth - 1 is through a temporal gateway in a research facility, which Schott plans to blow up to strand Dark Arrow (Oliver's Earth - X doppelgänger) on Earth - 1 . Oliver disguises himself as Dark Arrow to infiltrate the facility and discovers the Nazi doomsday device against parallel Earths is a militarized timeship called Wellenreiter . Barry and Ray battle the Freedom Fighters' Red Tornado to stop it from destroying the gateway while the rest of the team enters the facility to reactivate its portal, during which Stein is shot and gravely wounded . On Earth - 1, Eobard Thawne prepares to perform surgery on Kara to save Overgirl . Felicity and Iris try to stop him, but are captured . </P> This episode continues a crossover event that begins on Supergirl season 3 episode 8 and Arrow season 6 episode 8, and concludes on Legends of Tomorrow season 3 episode 8 . </Td> </Tr> <Tr> <Th> 78 </Th> <Td> 9 </Td> <Td> "Don't Run" </Td> <Td> Stefan Pleszczynski </Td> <Td> Sam Chalsen & Judalina Neira </Td> <Td> December 5, 2017 (2017 - 12 - 05) </Td> <Td> T27. 13409 </Td> <Td> 2.22 </Td> </Tr> <Tr> <Td_colspan="8"> While out Christmas shopping, Barry is ambushed and kidnapped by DeVoe while Caitlin is kidnapped from Jitters by Amunet . Iris claims they have to look for both of them, despite Harry's claim that they have insufficient time and resources and that they can only afford to search for one . Barry is held in DeVoe's lair . Caitlin is forced by Amunet to perform surgery on a metahuman named Dominic Lanse, who can read minds . They try to escape, but Amunet blocks their exit . Caitlin manages to briefly incapacitate Amunet, and she and Dominic flee the building they are being held in . Once outside, they are rescued by Cisco and Ralph, as Iris has chosen to focus on finding Caitlin . Barry manages to escape from DeVoe . Team Flash celebrates Christmas at the West house and Dominic joins them . Barry gets a security alert from his apartment . When he arrives, he receives a phone call from Dominic, who reveals that Amunet re-kidnapped Dominic and DeVoe has transferred his consciousness into Dominic's body . Barry discovers DeVoe's original body dead on his apartment floor and he realizes DeVoe has framed him for his "murder"; the police arrive, and Barry lets himself get arrested, not wanting to leave Iris again . </Td> </Tr> <Tr> <Th> 79 </Th> <Td> 10 </Td> <Td> "The Trial of The Flash" </Td> <Td> Philip Chipera </Td> <Td> Lauren Certo & Kristen Kim </Td> <Td> January 16, 2018 (2018 - 01 - 16) </Td> <Td> T27. 13410 </Td> <Td> 2.51 </Td> </Tr> <Tr> <Td_colspan="8"> Barry stands trial for the murder of Clifford DeVoe, with Cecile representing him . Cisco and Joe have to leave during the trial for a meta investigation, in which a meta caused people to collapse . Singh reveals to Joe he is appearing as a witness for the prosecution against Barry . The meta is eventually discovered as Neil Borman, who is a meta who produces radiation, which is causing the illness and collapsing . Barry takes him on, but is ill equipped to deal with the situation . Cisco and Killer Frost travel to the scene where Caitlin tries to freeze Borman, who quickly defrosts and incapacitates Caitlin . Barry creates a vacuum seal around Borman to contain the radiation, with Cisco transporting the radiation to the dead Earth - 15, draining the meta and defeating him . Barry is eventually found guilty by the jury and is sentenced to life in prison . </Td> </Tr> <Tr> <Th> 80 </Th> <Td> 11 </Td> <Td> "The Elongated Knight Rises" </Td> <Td> Alexandra La Roche </Td> <Td> Sterling Gates & Thomas Pound </Td> <Td> January 23, 2018 (2018 - 01 - 23) </Td> <Td> T27. 13411 </Td> <Td> 2.12 </Td> </Tr> <Tr> <Td_colspan="8"> Barry uses his speed to secretly help the guards contain the other inmates during a prison riot . He also befriends Dave Ratchet, his father's former cellmate . The next day, Barry meets Axel Walker who was later broken out of prison by his mother Zoey Clark, his father's one - time partner Prank . Axel challenges Ralph by threatening to cause chaos in the city . Ralph attempts to stop him but is wounded by Axel and is evacuated by Cisco . Ralph sneaks into the prison to talk to Barry about how scared he is . Barry reassures him that being a hero isn't about not being scared, but about having the ability to rise above your fear . Cisco and Caitlin go to rescue the hostages, but get captured by Axel and Zoey, who intend to kill them . Ralph arrives, and attempts to shield the two from an acid shower, until Wells manages to hack into the shower system to neutralize its acidity . Iris visits Barry in prison, where they reaffirm their love for each other . Ralph and Cisco go to get coffee, where they meet the excitable girl from the wedding . The girl writes in her journal, where she appears to be writing in the language Barry was using when he came out of the Speed Force . </Td> </Tr> <Tr> <Th> 81 </Th> <Td> 12 </Td> <Td> "Honey, I Shrunk Team Flash" </Td> <Td> Chris Peppe </Td> <Td> Sam Chalsen & Judalina Neira </Td> <Td> January 30, 2018 (2018 - 01 - 30) </Td> <Td> T27. 13412 </Td> <Td> 2.60 </Td> </Tr> <Tr> <Td_colspan="8"> Cecile develops telepathic abilities as a result of her pregnancy, combined with dormant dark matter in her cells, which Caitlin assures her should be temporary . In prison, Barry learns that Ratchet is innocent of a robbery - homicide that was actually committed by Sylbert Rundine fifteen years prior . Barry asks the team to look into the case . Rundine turns out to be a bus meta with the ability to shrink and enlarge objects, and he shrinks Cisco and Ralph while escaping . Harry's attempted cure backfires, and Caitlin determines that if they are not re-enlarged within a certain period of time, their bodies will explode . The team confronts Rundine at a warehouse, where Harry tricks him into re-enlarging Ralph and Cisco . Rundine is arrested, but refuses to confess to the earlier crime . Barry gathers that even if Ratchet went free, he would be as unhappy in the city as he is in prison; he wishes to live in a secluded Chinese village called Jiaju, but fears he will never get there . Barry then uses his speed to take Ratchet to Jiaju, where he can live out his dream . After discovering Barry is the Flash, the prison's warden, Gregory Wolfe, locks Barry in his private metahuman wing, intending to sell him to Amunet . </Td> </Tr> <Tr> <Th> 82 </Th> <Td> 13 </Td> <Td> "True Colors" </Td> <Td> Tara Nicole Weyr </Td> <Td> Jonathan Butler & Gabriel Garza </Td> <Td> February 6, 2018 (2018 - 02 - 06) </Td> <Td> T27. 13413 </Td> <Td> 2.28 </Td> </Tr> <Tr> <Td_colspan="8"> Wolfe plans to sell Barry and the imprisoned bus metas (Ramsey Deacon, Becky Sharpe, Mina Chaytan, and Sylbert Rundine) to Amunet, so they plan to escape . Cecile discovers Wolfe's plans after reading his mind . Ralph encounters a former colleague and his negative interaction with him prompts the discovery that he can shapeshift . His lack of mastery of the new ability prevents his attempt to foil Amunet's deal with Wolfe . Barry helps the metas escape the power dampeners, but they are cornered by Wolfe and Amunet . DeVoe arrives and again uses his chair to extract the metas' abilities, before transferring his mind into Sharpe's body . He then crushes Wolfe's skull as Marlize looks on in horror; Amunet flees . Ralph uses his shapeshifting ability to appear as the original DeVoe at Barry's appeal, claiming that he was unconscious at Barry's loft but not dead, which clears Barry's name . Team Flash realizes that DeVoe is only stealing powers from metahumans who were on the bus when the dark matter wave was unleashed, which means he will likely target Ralph as well . Back at the DeVoes' house, their marriage continues to deteriorate, and DeVoe drugs his wife with the Weeper's tears to maintain her devotion towards him . </Td> </Tr> <Tr> <Th> 83 </Th> <Td> 14 </Td> <Td> "Subject 9" </Td> <Td> Ralph Hemecker </Td> <Td> Mike Alber & Gabe Snyder </Td> <Td> February 27, 2018 (2018 - 02 - 27) </Td> <Td> T27. 13414 </Td> <Td> 2.12 </Td> </Tr> <Tr> <Td_colspan="8"> Barry is put on indefinite leave at the CCPD due to his connection with the DeVoe case . The team encounter another bus metahuman named Izzy with sound wave abilities, amplified by her violin . She manages to use her abilities when DeVoe (inside Sharpe's body) comes to claim her . Barry and Ralph help to train Izzy to refine her abilities, which proves difficult when she gets hurt . Eventually DeVoe shows up once again, using Dominic's and Becky's abilities to make Barry experience a brain aneurysm, while using Rundine's abilities to incapacitate Ralph . DeVoe then once again uses the chair to transfer his mind into Izzy's body and escapes . Both Ralph and Barry comfort each other over their respective losses: Barry being let go from the police force and Ralph losing Izzy to DeVoe . These losses enforce both Barry's and Ralph's determination to bring DeVoe down and save the three remaining metas . </Td> </Tr> <Tr> <Th> 84 </Th> <Td> 15 </Td> <Td> "Enter Flashtime" </Td> <Td> Gregory Smith </Td> <Td> Todd Helbing & Sterling Gates </Td> <Td> March 6, 2018 (2018 - 03 - 06) </Td> <Td> T27. 13415 </Td> <Td> 2.04 </Td> </Tr> <Tr> <Td_colspan="8"> Jesse comes to Earth - 1 to have a talk with her dad . Eco-terrorist Veronica Dale sets off a nuclear bomb, which Barry tries to stop, entering a form of superspeed known as Flashtime, where everything is frozen . However, the bomb has already detonated, and he and Jesse cannot stop it or save everyone with superspeed . Jay Garrick comes from Earth - 3 to help, but they are still unable to stop it . Barry remains in Flashtime for hours, bringing each of his friends into it, in an attempt to find a solution; they discuss options such as freezing it or sending it to another Earth, but none of those solutions prove to be viable . Eventually, Iris gives him the idea to retrieve the Quark Sphere from the Speed Force to send a blast lightning through the bomb, enough to disable it . Barry does so, and throws the Sphere back into the Speed Force, saving Central City . Jay admits he is retiring and going to train a new "female" speedster . Jesse and Jay return to their Earths, and Caitlin and Wells go for a coffee, where they encounter the mysterious girl . </Td> </Tr> <Tr> <Th> 85 </Th> <Td> 16 </Td> <Td> "Run, Iris, Run" </Td> <Td> Harry Jierjian </Td> <Td> Eric Wallace </Td> <Td> March 13, 2018 (2018 - 03 - 13) </Td> <Td> T27. 13416 </Td> <Td> 2.09 </Td> </Tr> <Tr> <Td_colspan="8"> A metahuman with fire powers tries to rob Central City bank . Another bus meta named Matthew Kim touches the metahuman, which causes his powers to transfer to another individual . When Joe, Iris and Barry turn up to ask Kim a few questions, Barry and Iris come into contact with Kim, causing Barry to lose his speed and Iris to gain superspeed . Inspired by Thawne, Harry plans to build his own thinking cap to outwit DeVoe . With their roles reversed, Iris becomes Central City's hero speedster, while Barry must learn to act as team leader . The new metahuman demands money and terrorizes the city with his fire powers . Using Wells' thinking cap, the Team comes up with the idea for Iris to create a tidal wave, negating the flames and defeating the meta . Back at S.T.A.R. Labs, Kim touches Iris and Barry again, restoring the Flash's speed . At home, Iris admits that while she did enjoy having superspeed, Central City needs the light that Barry was, and she is happy being team leader . Wells uses his thinking cap once more, determining the final two bus metas are Janet Petty and Edwin Gauss . </Td> </Tr> <Tr> <Th> 86 </Th> <Td> 17 </Td> <Td> "Null and Annoyed" </Td> <Td> Kevin Smith </Td> <Td> Lauren Certo & Kristen Kim </Td> <Td> April 10, 2018 (2018 - 04 - 10) </Td> <Td> T27. 13417 </Td> <Td> 1.82 </Td> </Tr> <Tr> <Td_colspan="8"> Barry and Ralph train to defeat DeVoe, with Barry becoming annoyed at Ralph's apparent inability to be serious . The team manages to locate another bus meta, Janet Petty . When Barry and Ralph confront her, it is revealed that Petty can manipulate a person's gravitational pull, which she demonstrates on Barry . Fearing once again that Ralph is not taking things seriously, Barry refuses to work with him . Ralph reveals his comedic attitude is due to a difficult childhood where his father abandoned him, causing him to make jokes whenever he is scared or under pressure . Barry relents and they go to stop Janet at a gala event . Janet uses her powers on Barry, causing him to float into the atmosphere . Barry tells the team to trust Ralph to improvise . Ralph detains Janet, then becomes a giant airbag to allow Barry to land safely . DeVoe's wife discovers he has been drugging her, so she will continue to assist him . Breacher comes to Earth - 1 to ask Cisco for help as some of his powers have failed . Harry takes the thinking cap to Thawne's time vault to recharge it and activates Gideon . </Td> </Tr> <Tr> <Th> 87 </Th> <Td> 18 </Td> <Td> "Lose Yourself" </Td> <Td> Hanelle Culpepper </Td> <Td> Jonathan Butler & Gabriel Garza </Td> <Td> April 17, 2018 (2018 - 04 - 17) </Td> <Td> T27. 13418 </Td> <Td> 1.88 </Td> </Tr> <Tr> <Td_colspan="8"> Team Flash track down the final bus meta Edwin Gauss, but are followed by the Samuroid, who injures Caitlin . The team rush back to Star Labs to regroup and heal . Caitlin reveals to Iris that Killer Frost is activated by her adrenal gland, and she is working on a way to separate them . Harry comes up with a tuning fork weapon that mimics Izzy's abilities in order to defeat DeVoe . Ralph reveals to Barry that he isn't afraid of losing his own life, but of Team Flash losing theirs, as he considers them family . Wells is shown to be addicted to the Thinking Cap, which Joe helps him deal with . Ralph takes the fork, with the intent to go with Edwin to kill DeVoe, which Barry argues against . Eventually, DeVoe manages to take over Edwin's mind, and as well takes the abilities of Janet Petty and Matthew Kim, before transferring his mind into Ralph's body . The team try to stop him, but DeVoe incapacitates them, and alters Caitlin's DNA, removing the dark matter and Killer Frost, before leaving . Back at his lair, DeVoe uses Ralph's morphing abilities to morph back into his original form, while he and Marlize plan their next move to destroy Team Flash . </Td> </Tr> <Tr> <Th> 88 </Th> <Td> 19 </Td> <Td> "Fury Rogue" </Td> <Td> Rachel Talalay </Td> <Td> Joshua V. Gilbert & Jeff Hersh </Td> <Td> April 24, 2018 (2018 - 04 - 24) </Td> <Td> T27. 13419 </Td> <Td> 1.90 </Td> </Tr> <Tr> <Td_colspan="8"> With DeVoe moving forward with his plans, Team Flash decide to secure Neil Borman . Barry and Cisco travel to Earth - X to recruit Leo Snart as a backup, but are followed to Earth - 1 by the Earth - X doppelganger of Laurel Lance . Team Flash plan to deliver Borman to a safe ARGUS facility, using a suit to contain the radiation, with Snart on hand, in case Borman goes nuclear . Snart agrees to help, but claims he can only stay for 24 hours, as he is due to get married to Ray Terrill . DeVoe attempts to intercept the transfer, but he and Team Flash are further ambushed by Earth - X Laurel, who kidnaps Caitlin, Borman and Joe, holding them at CCPD . Snart learns about Ralph, and convinces Barry to allow himself to grieve his fallen allies, which Barry eventually does, giving him strength to defeat Laurel . Lyla transfers Borman to another facility and Leo returns to Earth - X . Cisco and Wells come up with a plan to boost Wells' thinking cap . DeVoe goes more into his "god - complex"; stating that human emotion is a weakness, causing Marlize to doubt him . </Td> </Tr> <Tr> <Th> 89 </Th> <Td> 20 </Td> <Td> "Therefore She Is" </Td> <Td> Rob J. Greenlea </Td> <Td> Sterling Gates & Thomas Pound </Td> <Td> May 1, 2018 (2018 - 05 - 01) </Td> <Td> T27. 13420 </Td> <Td> 1.70 </Td> </Tr> <Tr> <Td_colspan="8"> DeVoe starts gathering the technology required to build the Enlightenment Machine, including murdering anyone who gets in his way . Barry, Cisco, Iris and Harry attempt to trigger Killer Frost's powers in Caitlin, but do not succeed . Harry reveals to the team that the amount of dark matter he used with the Thinking Cap caused brain damage . Cisco, Gypsy, Barry and Caitlin fight Marlize and DeVoe when they acquire the computers required to power the Enlightenment Machine . Flashbacks reveal partially why Marlize follows DeVoe: she was a humanitarian worker in Kenya who created a water purifier for a villager, but when warlords found out about it, they attacked and killed everyone . Marlize pleads with DeVoe when he begins choking Gypsy; she later decides to leave him, encasing his chair in a force - field so DeVoe cannot stop her from leaving the pocket dimension . The team realizes that DeVoe plans to use the Enlightenment Machine to launch dark matter towards Earth, reverting all of humanity into a simplified state, similar to what Harry is dealing with . The mysterious girl brings a gift to Cecile and Joe's baby shower and, after leaving quickly, runs away using speedster abilities . </Td> </Tr> <Tr> <Th> 90 </Th> <Td> 21 </Td> <Td> "Harry and the Harrisons" </Td> <Td> Kevin Mock </Td> <Td> Judalina Neira & Lauren Certo </Td> <Td> May 8, 2018 (2018 - 05 - 08) </Td> <Td> T27. 13421 </Td> <Td> 1.74 </Td> </Tr> <Tr> <Td_colspan="8"> Cisco assembles a Council of Harrisons to try and come up with a way of stopping Harry's intelligence loss . Team Flash reluctantly go to Amunet for help, encountering her successor Norvok in the process, though Barry insists Amunet must not kill . The team is eventually given a bomb made from Amunet's metal which will be capable of destroying one of DeVoe's satellites, and Harry manages to work out that DeVoe's plan might be changing because Marlize is no longer with him . Iris posts an article revealing DeVoe's plan and the residents of Central City begin reporting DeVoe sightings, which Iris believes will hamper his ability to remain undetected . </Td> </Tr> <Tr> <Th> 91 </Th> <Td> 22 </Td> <Td> "Think Fast" </Td> <Td> Viet Nguyen </Td> <Td> Sam Chalsen & Kristen Kim </Td> <Td> May 15, 2018 (2018 - 05 - 15) </Td> <Td> T27. 13422 </Td> <Td> 1.93 </Td> </Tr> <Tr> <Td_colspan="8"> DeVoe infiltrates the A.R.G.U.S. facility holding Fallout by impersonating John Diggle and kills most of the security, except for a few hostages; overcharging and killing Fallout to be a nuclear battery for the satellites . Barry runs to Star City and brings back John to reveal the location of the facility . Caitlin and Cisco ask Barry to train them in Flashtime so that they can save the hostages and Barry can follow DeVoe through the breach before it closes . In the last stages of pregnancy, Cecile's telepathy causes her to take on the personality and thoughts of anyone nearby . Harry and Iris track Marlize to London, and use the last extrapolator to get there . Caitlin and Cisco are able to rescue the hostages . Searching her mind for Killer Frost, Catlin has Cisco vibe her into a repressed memory of a childhood accident; Killer Frost was already part of Caitlin decades before the particle accelerator had created any metas . Barry manages to follow DeVoe through the breach and destroys one of the satellites with Amunet's bomb . DeVoe takes control of S.T.A.R. Labs and uses its satellite to replace the one destroyed . He initiates the Enlightenment protocol in the time vault . </Td> </Tr> <Tr> <Th> 92 </Th> <Td> 23 </Td> <Td> "We Are the Flash" </Td> <Td> David McWhirter </Td> <Td> Todd Helbing & Eric Wallace </Td> <Td> May 22, 2018 (2018 - 05 - 22) </Td> <Td> T27. 13423 </Td> <Td> 2.16 </Td> </Tr> <Tr> <Td_colspan="8"> After the Enlightenment begins, Marlize joins Team Flash as Cecile goes into labor . Marlize uses Cecile's powers to send Barry into DeVoe's consciousness to find the good left in him . Barry finds Ralph alive in DeVoe's consciousness and together they find the "good" DeVoe dead . DeVoe attempts to keep them from reaching the nexus of his mind, as he follows Team Flash to a pocket dimension . In his consciousness, DeVoe multiplies himself to fight Barry and Ralph as he takes down Team Flash . Barry and Ralph make it to the nexus; Barry wakes up in the real world and Ralph reclaims his body just as DeVoe was going to kill Cecile . He reappears, though, as a hologram through his chair until Marlize destroys it . Barry, Cisco and Ralph shield civilians from the falling satellites and the mysterious girl helps Barry destroy the last one . Harry's brain resets but is mostly restored by Marlize; he decides to return to Earth - 2 to be with Jesse . Team Flash celebrates DeVoe's defeat with Wally (who returned from the Legends) and Cecile's newborn daughter Jenna . The mysterious girl arrives to reveal herself as Barry and Iris' daughter from the future, Nora; she claims to have made "a big, big mistake". </Td> </Tr> </Table> <Tr> <Th> No . overall </Th> <Th> No. in season </Th> <Th> Title </Th> <Th> Directed by </Th> <Th> Written by </Th> <Th> Original air date </Th> <Th> Prod . code </Th> <Th> U.S. viewers (millions) </Th> </Tr>

When does the flash season 4 episode 15 air