In Mockingjay by Suzanne Collins, Peeta experiences dramatic changes at the hands of the Capitol. His torture at the hands of the vicious Capitol guards leaves him paranoid and broken. Katniss reels from his attempted strangling of her, wondering if he is in fact "deranged," but Plutarch and Haymitch suggest another descriptor for his condition, "hijacked" (179).
Using tracker-jacker venom, the Capitol has reconditioned Peeta to fear and loathe the sight of Katniss Everdeen. "The venom targets the part of the brain that houses fear," and Peeta has been brutally taught to fear Katniss as a muttation (188).
As the novel progresses, Peeta slowly gains recontrol of his mind thanks to the kindness of other characters, particularly Delly, a classmate of Katniss and Peeta's. Delly teaches Peeta a game, "real or not real," to help him define and understand his memories.
Collins reassures her readers at the end of the novel as Katniss reflects that Peeta is like "the dandelion in the spring...the bright yellow that means rebirth" (388); Katniss' comparison shows Peeta as being wholesome and hopeful, recovered from his traumatic experience.