In the upcoming episode of "Pretty Little Liars" season 7, one of the Liars will be blackmailed by A.D. into helping her archenemy.

Titled "In the Eye Abides the Heart," next week's episode will see a Liar help her nemesis in exchange for her friends' security. According to the official synopsis, one of the Liars falls into A.D.'s trap and starts giving information to the dark side. Aria (Lucy Hale) gives an ultimatum to Ezra (Ian Harding) about Nicole (Rebecca Breeds), while Emily (Shay Mitchell) figures out a way to support Ali (Sasha Pieterse).

Meanwhile, Hanna (Ashley Benson) learns shocking information about Lucas, which forces her to set out on a mission to prove his innocence. Spencer (Troian Bellisario) goes out of her way to meet up with Mary (Andrea Parker) and unexpectedly encounters Wren (Julian Morris). Marco (Nicholas Gonzalez) suspects the Liars know something about Archer's (Huw Collins) disappearance, and another person is brought in on A.D.'s game.

The promo shows Marco confronting Spencer about the theories he has against the Liars. One of the Liars is in serious danger and Aria decides to betray her friends. She appears shocked after opening a locker with A.D.'s black jacket.

Last week's episode titled "Power Play" finally revealed who murdered Jessica (also played by Parker). Peter (Nolan North) said Jessica's twin sister Mary was the one who killed Ali's mom and buried her in the Hastings family's backyard. Although one mystery had been solved, Peter's revelation only opened up more questions for viewers.

Speaking with TV Guide, Parker teased that Mary will soon find out about Ali's pregnancy. "She's going to have to deal with it. I think that Mary is still misunderstood," Parker said. "There's still a lot more to be revealed about why Mary behaves the way that she does. I think that her love for Spencer and Alison is deep and genuine."

The seventh and final season of "Pretty Little Liars" airs every Tuesday at 8 p.m. EDT on Freeform.