<P> Waking up in Carter's bed again, Tree convinces Carter of her predicament by showing that she holds knowledge of the day's events . Tree tells him that she hates who she has become since distancing from her father after her mother's death . Later, Tree sees a local news report on John Tombs, a serial killer being held at the campus hospital . Concluding that Tombs is her killer, Tree rushes to the hospital to warn of his escape . Tombs breaks free and nearly kills Tree, but Carter follows and rescues her . Tombs kills Carter before chasing Tree to a nearby bell tower where she manages to subdue him with a crowbar . Realizing that Carter will remain dead if she ends the loop, Tree hangs herself . </P> <P> Believing she has solved her murder, Tree is happier and more relaxed during the next loop . Tree ends her affair with Butler and meets with her father . That night, she goes to the hospital and attacks and kills Tombs . Relieved to finally be free, she celebrates her birthday in Carter's room and eats the cupcake given to her by Lori . </P> <P> Tree wakes up in another loop . Confused and angry that the time loop continued after she killed Tombs, Tree returns to her room where Lori offers the cupcake again . Tree realizes this was the only time she had ever eaten the cupcake and died in her sleep . Tree deduces that Lori is the true killer; Lori had poisoned the cupcake, but when Tree declined to eat it, she utilized her job as a nurse in the hospital to drug and frame Tombs for Tree's murder . Tree tries to coerce Lori to have a bite, however when Lori refuses, Tree decides to take the cupcake to the police . Lori lunges at Tree, locks the door and confesses that she was jealous of Tree's affair with Butler, before engaging in a fight . Tree manages to stuff the cupcake in Lori's mouth before kicking her out of a window, sending her falling to her death . </P> <P> Tree and Carter muse over the day's events in a restaurant . He offers her his room for the night, and Tree wakes up the next day believing herself to be in another loop . Carter reveals it to be a prank, and the two kiss . </P>

Who is killing her in happy death day