Plot

When a contract killer has a rapidly evolving form of dementia, he is offered an opportunity to redeem himself by saving the life of his estranged adult son.

When a contract killer is diagnosed with a fast-moving form of dementia, he is presented with the opportunity to redeem himself by saving the life of his estranged adult son. To do this, he must race against the police closing in on him, as well as the ticking clock of his own rapidly-deteriorating mind.

John Knox works a day-to-day job as a contract killer employed by Jericho, a crime boss. He is estranged from his wife and son and lives alone, only interacting with other members of his industry and Annie (Joanna Kulig), the Polish sex worker who comes to visit him once a week, who shares his love for books. Knox is diagnosed with a fast-moving form of dementia called Creutzfeldt-Jakob disease and quickly makes arrangements to cash out and retire from the business. Before that, he undertakes one last job with his partner, Thomas Muncie.

During the job, after successfully killing his target but also unintentionally killing the woman who was with him in the shower, Knox accidentally kills Muncie in his dementia-fueled confusion. He quickly stages the scene and leaves. That night, he is unexpectedly visited by his estranged son, Miles, who tearfully admits to killing a man for raping his daughter, Knox's granddaughter. Knox instructs his son to remain quiet to the authorities as he later arrives at the crime scene and meticulously removes evidence that may incriminate Miles, while mysteriously storing them away for later use. Meanwhile, dogged detective Emily Ikari is on both murder cases, determined to pinpoint the perpetrator.

Knox later visits his friend Xavier Crane, a former thief. Together, they cook up a plan to set Knox's family up for life while leaving the business behind, all while Knox battles his fading mental state. Meanwhile, Detective Ikari links both crimes to a single perpetrator. She interrogates Knox to no effect. He plants the evidence he had previously stored away around his son Miles' home, seemingly betraying him. Miles is arrested for the murder of his daughter's rapist, and is confronted by Knox in prison, where Knox accuses Miles of ratting him out in a tax evasion case several years prior.

After getting lost in the woods after digging up his stash of diamonds at a cabin his family used to own, Knox is picked up by Crane and driven home. Upon reaching home, he is confronted by a group of burglars and Annie, who had become aware of Knox's dementia and the fact that he had been cashing out and ratted him out as a result. Killing them all, Knox confronts Annie at gunpoint and informs her that she would have gotten a share anyway.

Despondent, Knox calls Xavier, who wishes him fortune before informing the police as part of their plan, whereupon he is arrested by Detective Ikari. The police later discover signs that the evidence found at Miles Knox's house may have been tampered with, and planted there by Knox, leading to the conclusion that Knox may have framed his own son for the murder. When asked by Ikari on a possible motive, Miles, recalling his father's accusation of him in prison, responds accordingly, shifting the blame fully over to Knox. He is then released.

Several weeks later, Miles visits his father in prison. Knox, now having fully lost his mental faculties, does not recognize his own son and is later moved from prison to a medical facility, having only weeks left to live. Miles and his mother receive equal shares of Knox's fortune, ensuring the completion of his retirement plan. Annie, who is spared, is shown receiving Knox's library and opening the cover of A Tale of Two Cities. The film ends with a catatonic Knox staring out a window.