Person of Interest Wiki
Person of Interest Wiki
Episode Overview   Summary   POI   Cast and Characters   Crew    
← Season 2 Person of InterestSeason 3 (Flashbacks in parentheses) Season 4 →
301Liberty 309The Crossing 317Root Path (/)
302Nothing to Hide 310The Devil's Share” (Multiple) 318Allegiance
303Lady Killer 311Lethe” (Finch) 319Most Likely To...
304Reasonable Doubt 312Aletheia” (Finch) 320Death Benefit
305Razgovor” (Shaw) 3134C 321Beta” (Grace)
306Mors Praematura 314Provenance 322A House Divided” (Collier)
307The Perfect Mark 315Last Call 323Deus Ex Machina” (Collier)
308Endgame” (Carter) 316RAM

POI 0311 Main.png



Air dateDecember 17, 2013

Running time

Production code2J7611

Written byErik Mountain

Directed byRichard J. Lewis


Images (52)

There was a second machine, and Arthur built it.

— Finch

"Lethe" is the 11th episode of season 3, and the 56th produced hour of Person of Interest. It originally aired on December 17, 2013.


Flashbacks to Finch’s adolescence provide insight into his creation of the Machine. The team receives the number of a man dying of a brain tumor as Reese leaves the POI team behind in the aftermath of the war with the crime organization, HR.

Origin of the Title

Lethe (Λήθη) in Greek mythology is the river of forgetfulness. It is one of the five rivers flowing into the Hades, the Underworld; drinking its waters causes the drinker to forget. It is also the name of the goddess of forgetfulness. 

Main Plot Points

  • Following the death of Carter, Reese quits the team and travels to Colorado followed by Fusco. After a brawl, the two are arrested.
  • When Finch ignores it, the Machine sends a number to him through Root, communicating with her despite her Faraday cage confinment and lack of electronic devices.
  • Finch discovers the number belongs to Arthur Claypool, an old MIT friend of his who is terminally ill with a brain tumor that causes memory problems.
  • After fleeing Peter Collier and Vigilance, Arthur reveals that he worked on Samaritan, a second Machine for the government before the project was shut down.
  • Arthur's wife Diane is exposed as a fraud and she calls in ISA agents including Hersh.
  • Diane reveals herself to be Control, Shaw's mysterious former boss. Though Samaritan was shut down and destroyed, Control demands to know the location of "the drives" and threatens both Arthur and Finch for the locations of the respective Machines.
  • The Machine calculates the status of Samaritan, changing it from Deactivated to Unknown and calculating the possibility of a Systems Conflict between them.


  • In 1969 a young Finch looks out at some birds flying nearby and asks his father about them. Finch's father agrees to tell him about the birds if Finch helps him fix his truck. While his father answers a phone call, Finch takes apart the truck's carburetor and locates the problem, telling his father that if things weren't made to be taken apart they should be built better. Finch's father also displays signs of memory loss.
  • In 1971 Finch shows his father a device he has built and states that he intends to build something that can remember the things his father no longer can. Finch suggests that someday he will build a machine that will have lots of memory space and can think for itself, but his father tells Finch that even if he can, that machine won't be him and that something's aren't meant to be fixed.
  • In 1979 a teenage Finch hangs out with his friends and for fun causes a "Phone Phreak" that enables a nearby payphone to call Paris. As he and his friends laugh, a police officer pulls up and asks Finch to come with him, saying he's got his father who the cop has in the backseat.
  • The police officer returns Finch and his father home and tells Finch that his father had wandered half a mile away before he found him. The police officer suggests that Finch find a place for his father that can take care of his needs before driving away. Finch's father apologizes for the effects his deteriorating memory loss is causing and suggests that Finch leave him to go to college as Finch is too smart not to. Finch tells his father that a computer network is being built to connect colleges across the country and he will use it to get the knowledge he needs. Finch quotes what he told his father ten years before about how if someone doesn't want someone else to get inside something, it should be built better causing them both to laugh.

Episode Notes

  • Sodium Pentothal is a barbiturate used for anesthesia, and in small doses, as a "truth serum". It is identifiable by its strong odor of garlic and onions, which Shaw detected when she sniffed the syringe.
  • According to the PET computer, the episode takes place on Dec 17, 2013, the original airdate of the episode.
  • Root received the number instead of Finch, this indicates that Root has a way to communicate with the Machine without the use of a telephone.
  • When the Machine begins calculating the possibility of Samaritan's reactivation, it also brings up evaluations of other real intelligence programs, including Able Danger, Genoa, Genoa II, Fairveiw, Bullrun, and PRISM. The first three are listed as "deactivated" while the latter are described as "active decoys" to Northern Lights.
  • This episode is the first part of a two episode mini-arc; the POI and storyline of this episode carry over into the next episode, “Aletheia”.
  • This episode is the beginning of the Samaritan arc, an arc that continues to the series finalie “return 0”.

Production Notes

  • POI 0311 Control1.png
    This episode includes the first appearance of Control. The alert viewer might have seen a red box appear around her when she exits the elevator during their escape the hospital. She only appears on screen for half a second.

Bloopers and Continuity Errors

  • The number that Root gives Finch (229-00-8003) is different than the number on Arthur's medical records (XXX-XX-9019). The former one was also Nicholas Donnelly's number in “Prisoner's Dilemma



  • The bartender at the Roadhouse is the actual bartender and not an actor.[1]
  • When the Machine tries to predict the outcome of the situation at the end of the episode, it says that the names: Sameen Shaw and Robert N. Hersh are aliases.
  • Also when predicting outcomes, in the lower right corner on the screen we can see that the Machine is "Retasking Analog Interface", which is Root.
  • Again in the Machine's predictions, when it calculates the probability of operational conflicts with Samaritan, we can see for less than a second that there is a 37.16% probability of a Russian Revolution and that the nuclear proliferation in Iran is at 25.28%.
  • Flashbacks in this episode indicate that Harold is an only child, which means the story he told Joss Carter in the episode Super about his brothers throwing him into the deep end to teach him how to swim was just something he made up and not an actual story of his past.


  • "Not sure I like being associated with your former employers, who tried to kill you." (Finch, to Shaw)
  • "Should I be looking for some action elsewhere?" (Shaw, to Finch)
  • "Your sure you don't want to play MD Harold? I never made a convincing doctor even when I was one." (Shaw)
  • "If they don't want you to get inside, they ought to build it better." (Young Finch)
  • "He is not deceived, who knows himself to be deceived." (Arthur)
  • "If I keep working on it, I think I can make it so it can remember all the things you can" (Young Finch, to Finch's father) "Now, we talked about this. I mean, what's wrong with me can't be fixed by you, or anyone else, okay?" (Finch's father, to Young Finch)
  • "But what if I build a machine with lots of memory, one that could think?" (Young Finch) "Even if you could... even if you could fill it with all my memories, it still wouldn't be me. Not everything that's broken is meant to be fixed, understand?" (Finch's father)
  • "Dude, that was too much fun to be legal." (Finch's friend)
  • "It just proves that no matter what we do or don't do in this world, bad things are going to happen. It's pointless. Irrelevant." (Reese)
  • "The truth fears no questions." (Arthur)
  • "One of you is going to tell me what it is I want to know. And whoever does, will be the one who gets to leave here... alive." (Control)
  • "The kind you need a gun for." (Shaw, regarding what kind of people were pursuing Arthur)
  • "Talking is overrated... I mean, that must have been really hard." (Shaw, to Arthur's wife)
  • "What do you think, I won my detective shield in a poker game?" (Fusco, to Reese)
  • "Well, if they don't want you to get inside...they ought to build them better." (Young Finch, to Finch's father)