<Li> Real identity: Mona Vanderwaal . </Li> <P> Three year after the disappearance of Alison DiLaurentis, her four friends, Aria Montgomery, Spencer Hastings, Emily Fields, and Hanna Marin, each receive messages from someone calling themselves "A ." The girls had drifted apart over the years, so they had no idea that other people were getting texts as well . Additionally, the texts were about secrets only Ali knew about . At first, the messages were simply teasing and all of the girls wonder if their missing friend was the one who sent them . Though they knew she was most likely dead, she was still the only one who knew their darkest secrets . Once Ali's body is discovered in her old backyard, the girls are even more baffled when they continue to receive threats . At Ali's funeral, the girls are reunited and they find out that they've all been receiving weird messages . As the girls stand outside after the funeral ends, they all get a text saying, "I'm still here, bitches . And I know everything .--A". </P> <P> From that point on, the messages take on a distinctly more threatening tone . Aria is given an ultimatum to tell her mother about her father's affair by midnight after the Foxy event, or A will do it for her . A continues to play life - altering games with the girls, from encouraging suspicion of Spencer's involvement in Ali's death to outing Emily's sexuality to her conservative mother . However, A makes a serious mistake in texting Hanna on the night of Mona's birthday party . Instead of using the plain Blackberry she bought just for tormenting the girls, A accidentally uses his / her own phone . Hanna, who has a new phone without all of her contacts recognizes the number, compelling A to act before Hanna can reveal A's true identity to the others . A hits Hanna with an SUV, successfully destroying Hanna's phone and putting her into a coma that eventually leads to a temporary loss of memory . Soon after that, "A" puts a drug in Emily's pain cream which causes an Ulcer in the spot where she has been putting the cream . She ends up in the hospital and might not be able to swim again . </P> <P> A knew that there was a very good chance Hanna would regain her memory . Hanna's best friend, Mona Vanderwaal, informs the girls that she has also received texts from A, drawing the five closer together in trying to figure out who their tormentor is . Mona subtly encourages Spencer's fears that her sister, Melissa, might be A as well as Alison's killer . During Hanna's recovery masquerade celebration, she suddenly regains her memory, revealing that Mona is A. However, she, Emily, and Aria can't do much about it, because Spencer and Mona are on their way to the police station . After Spencer is warned about Mona by text, she tries to escape Mona's car, but Mona catches on rather quickly and diverts to a path in a more remote area of Rosewood . She tells Spencer everything, from seeing Ali launch a firework into Toby Cavanaugh's garage and blind her friend Jenna, to finding Ali's diary of secrets among a pile of old DiLaurentis junk the St. Germains left at the curb, discovering the girls' secrets that only Ali knew . Her motivation was to get revenge for her friend's blindness, even though Jenna and Ali had planned together to launch the firework . Mona didn't know this and got a scar on her stomach from the ordeal . Mona also drops the bombshell that Ian Thomas killed Ali, due to Ali's last diary entry about giving him an ultimatum to break up with Melissa . She then offers Spencer to become A with her and tell Hanna that she must not be remembering correctly, but she refuses . The two fight at Floating Man's Quarry and Spencer accidentally pushes Mona, who falls and has her neck caught between rocks . </P>

Who's on the a team in pretty little liars