Lethe (Person of Interest)

"Lethe" is the 11th installment of *Person of Interest*'s third season, marking the 56th episode overall. Co-producer Erik Mountain wrote it, with Richard J. Lewis directing. It first aired on December 17, 2013, via CBS in the U.S. and CTV in Canada. The episode pushes forward the series' central "Samaritan" plotline and delivers a major reveal about the character Control.

The story splits between past and present. In flashbacks, a young Harold Finch helps his father with a truck engine in 1969, later builds a memory aid for his father in 1971 after his father begins losing his memory, and in 1979 shows friends a trick for making a long-distance phone call before his disoriented father is brought home by police. In the present, John Reese has left the team without explanation after regaining consciousness. Finch initially ignores the Machine's numbers but, after a talk with Root, agrees to investigate the next one: Arthur Claypool, an IT consultant Finch recognizes from MIT. Claypool is hospitalized with a brain tumor and has memory issues. Shaw, posing as a doctor, learns he has Secret Service protection and overhears him mention "Samaritan." They discover Claypool worked for the NSA on Samaritan, a self-upgrading AI program that was supposedly destroyed in 2005 over civil liberty concerns. Shaw is detained by Agent Easton after infiltrating an MRI scan, but Easton is poisoned by Vigilance, who then force Shaw and Claypool's wife to extract him. Claypool doesn't recognize them until Finch arrives. After escaping Vigilance, Finch and Shaw take Claypool and his wife to a safe house. Meanwhile, Reese is in Colorado, frequenting a bar that belonged to his late father. Fusco finds him there, and after a conversation, they fight until arrested. At the safe house, Claypool remembers his wife died years ago, and the woman with them reveals herself as Control, Shaw's former ISA boss. Hersh and hitmen subdue the team, and Control demands either Finch reveal the Machine's location or Claypool reveal the location of Samaritan's source code, threatening to kill one of them. The episode ends with the Machine analyzing threats and changing Samaritan's status from "Deactivated" to "Unknown."

The episode drew an estimated 12.4 million U.S. household viewers and a 2.0/6 ratings share among adults 18–49, per Nielsen Media Research.