Stanton "Stan" Carlisle, having set his Midwestern home ablaze, embarks on a new chapter of his life as he takes up work with a traveling carnival. When Clem, the carnival owner, needs assistance in dealing with a sick geek, he turns to Stan for help in disposing of the unfortunate man. Witnessing the sordid reality of a geek's life—living in squalor and enduring the humiliation of biting off the heads of live chickens for entertainment—deeply disturbs him. Clem explains that he targets men with troubled pasts, often struggling with addiction, and entices them with the promise of a "temporary" job and opium-laced booze. This manipulative cycle ensures their dependence, leaving them with no choice but to remain trapped in their misery.
As Stan adjusts to his new surroundings, he becomes entangled in the act of Madame Zeena, portrayed by Toni Collette, and her alcoholic husband Pete, a role played by David Strathairn. Utilizing a clever coded language and cold reading techniques, they create the illusion of extraordinary psychic abilities. However, both Zeena and Pete warn him never to exploit their skills in a "spook show" that misleads patrons about the dead; it's crucial to reveal the ruse afterward to prevent harm.
In the carnival's hustle and bustle, Stan's heart is captured by fellow performer Molly, played by Rooney Mara, and he proposes they craft a two-person act separate from the carnival's unseemly nature. Tragedy strikes when Stan mistakenly administers the wrong alcohol to Pete, leading to the elder man's death from wood alcohol. This event propels Stan to declare his love for Molly, and they leave the carnival behind to pursue their ambitions.
Two years later, Stan has transformed himself into "The Great Stanton," a psychic performer for Chicago's wealthy elite, with Molly by his side. Their act, however, faces scrutiny when the astute psychologist Dr. Lilith Ritter interrupts, seeking to unveil their secrets. Stan's adept cold reading skills secure their performance, but Dr. Ritter remains undeterred, eventually testing his legitimacy at the behest of the affluent Judge Harrington.
Harrington, convinced of Stan's gifts, pays him to establish contact with his deceased son, disregarding Molly's disapproval of this unethical "spook show." Stan's relationship with Ritter grows complicated, morphing into a manipulative affair that spirals out of control. She exploits sensitive information from her therapy sessions, and together, they scheme to dupe Harrington further.
However, their charade leads Stan to Ezra Grindle, a powerful man yearning to communicate with his lost love, Dory, who tragically suffered a forced miscarriage. Ignoring Ritter's warnings about Grindle's volatile nature, Stan attempts to con him. The situation escalates, and when Molly, cast as Dory, discovers Stan's betrayal, she departs, leaving him vulnerable. Grindle, enraged by the deception, threatens both Stan and Molly, ultimately leading to Grindle's demise at Stan's hands.
Betrayed by Ritter, who has been pilfering his earnings and poised to expose him, Stan is left alone, injured, and hunted. Attempting to seek solace in a carnival, he is met with rejection until he is offered a final drink and the "temporary" job as the new geek. In a haunting admission of his broken spirit, Stan laughs and sobs as he resigns himself to his fate, declaring, > "Mister, I was born for it."
