Ulrich Kohl arrives in New York City, using the alias Wallace Nagel. Two German men discuss Kohl and figure that he knows everything and that they should take steps to take care of Kohl.
Kohl gets off at the train station and sees a German man, Heinlein, watching the crowd and trying to spot him. The newcomer quickly ducks into the crowd and slips away before Heinlein can see him.
At headquarters, Reese brings Finch a cup of green tea and half-jokingly assures his partner that he’s not trying to find out more about him. Finch has their new Person of Interest, Wallace Nagel. Nagel is a German immigrant who works in international expert, but hasn’t made any electronic transactions in the last 24 years. Reese figures that “Wallace Nagel” is a cover identity, while Finch confirms that “Nagel” purchased a cemetery lot in 1987, just before his disappearance.
Finch goes to see a book dealer, Pilcher, who keeps pre-digital records of government and covert information. He blackmails the dealer into helping him find information about Nagel’s real name, threatening to reveal Pilcher’s connection the recent sale of Soviet submarine schematics if he doesn’t help.
Reese visits the cemetery and finds Nagel’s grave. It has been recently dug up and the only thing left is a German mark lying in the dirt.
Pilcher tells Finch that the “Nagel” is actually Ulrich Kohl, a member of the East German intelligence agency, the Stasi. Kohl was part of a Stasi team that hunted down and neutralized East German defectors... permanently. Back at headquarters, Finch does some background checks and calls Reese to inform him that Kohl was in East Germany when the Berlin Wall fell. Kohl hid in the Soviet Union with his wife Anja, avoiding the American authorities, but she was killed in a car crash in 1987. Kohl then disappeared in 1989 when East Germany collapsed. Reese tells his partner that Kohl had an emergency cache of weapons and money buried in his “grave,” and that he has gone active again.
Kohl goes to the apartment of a man named Hauffe and shows him a photo of Anja. Hauffe realizes who Kohl is and Kohl shoots him in the shoulder. He then tells Hauffe that they have matters to discuss and steps into the apartment.
Reese arrives in Europe and meets with his female contact, Stanton. She offers him a drink and says that he’ll need a new name for covert ops and that she’ll figure out what it should be. Stanton warns him that now that he’s in a new line of work, there’s no way back to his old life. She asks him if he saw any old friends and shows him a photo from the airport where he met his ex-girlfriend, Jessica Arndt.
Finch checks the mark from the graveyard and confirms that it’s been out of circulation since 1990, and someone recently sold a collection at a rare coin store. He traces the address of the call that Kohl made from the store and gets Hauffe’s address. Reese arrives there and finds Hauffe, dead, and they figure that Kohl called Hauffe to make sure that he was at home. Hauffe has been recently interrogated judging by the pinpricks on his next. Finch checks Kohl’s files and learns that he worked with three other men on his team: team leader Steiller, document forger Wernick, and case officer Heinrich Hauffe. Reese searches Hauffe’s apartment and finds a pin, as well as hidden documentation confirming that Hauffe was a member of Kohl’s team.
Heinlein enters the apartment and tries to capture Reese, who easily knocks him out. He searches the man and confirms that Heinlein is with German Intelligence, and then calls Fusco to tell him about Hauffe’s death. Reese tells Fusco to interrogate Heinlein and then fires a shot so someone will call the police and give Fusco an excuse to get involved. As Reese leaves, he takes Hauffe’s phone and confirms that the last call was made to Wernick, who is in witness relocation as a Wall Street lawyer. Reese figures that Kohl is killing his teammates because he believes that they engineered Anja’s death and made it look like an accident.
Kohl tracks down Wernick to the café that he frequents and hits him with a poisoned needle. He then sits down from Wernick, who recognizes him immediately and realizes that he’ll soon be dead. Kohl shows him the photo of Anja and says that he promised her that she’d be safe, and that he’s paid in full for the sins of himself and his team. Since he was imprisoned, Kohl explains that he’s been planning his revenge. Wernick admits that what he and the others did was wrong, and tells Kohl to be at peace before he collapses dead.
Finch checks with Wernick’s assistant and learns where he is, and Reese gets to the café as Wernick dies. Reese steals the ambulance with Wernick and drives him to a safe location, and offers to save Wernick in return for information. Wernick tells him that his team was killing American informants, and that the team traded Kohl to the Americans in return for witness relocation. The Americans then went after Kohl and his wife, killing her in a car accident. As Reese gives Wernick the information, the man passes out before he can tell Reese the location of the last team member, Steiller.
Reese gives Finch the information from the pin he found in Hauffe’s apartment. Finch determines that it belongs to a New York German-American society and figures that Steiller, Wernick, and Hauffe were all members and used it to keep in touch.
Carter and Fusco bring in Heinlein and confirm that a man matching Reese’s description stole the ambulance. Heinlein refuses to talk until Carter points out that he’s on his own and has no leads on Kohl. The agent finally explains that the American and Germans conducted a joint operation 24 years ago to arrest Kohl. It was finally believed that he was too old to be a danger and transferred to a minimum-security facility. Kohl promptly escaped and the Germans want him back in jail before his existence creates an international incident. Heinlein prepares to tell them more but the liaison from the German Consulate arrives with orders from the State Department authorizing Heinlein’s release and extradition.
Finch hacks the German society’s website and confirms that one of the members, a construction foreman, matches Steiller’s description. He relays the information to Reese, who heads to Steiller’s construction site, and then calls Steiller. Steiller gets the call just as Kohl arrives to kill him. The foreman keeps the phone on but pockets it, and Finch and Reese listen as Steiller tells Kohl that he knew the assassin believed in the killing. Kohl points out that Steiller trained him and prepares to kill him, and Steiller says that there’s something he doesn’t know. Steiller says that he’s the only one who knows and then calls... Anja Kohl. The ex-spy explains that Anja located him a few years after they all defected, and that she was afraid of Kohl. Steiller tries to attack Kohl, who throws him over the edge of the building to his death. The assassin then leaves before Reese can get there, and Reese figures that Kohl is going after his ex-wife next.
As Heinlein is released, Fusco suggests to Carter that her mystery man is at least getting results, but she doesn’t agree. Fusco sends the consulate car’s GPS signal to Reese, who picks up Finch and gets ahead of the car on the route to the airport. Reese sets up a sniper rifle and has Finch act as his spotter, and then shoots the tires out of the German car. Reese grabs Heinlein and demands to know where Anja is. The German Intelligence operative says that he doesn’t know, but slips Reese a piece of paper with the address so that his superior doesn’t see it. Once the Germans leaves, Reese and Finch head for Anja.
Kohl goes to Anja’s apartment only to find Reese waiting for him. Reese tells him that Anja is safe and prepares to capture him, but Kohl manages to get the drop on him and knock him out with pressure to the carotid artery. Meanwhile, Finch prepares to take Anja to the police station and put her with Fusco, but she says that she has to make a call first.
Kohl prepares to torture the tied up Reese unless he reveals where Anja is. Reese refuses and Kohl prepares to torture him, unimpressed when Reese points out that he withstood torture for 16 hours in Kandahar. The German then inserts one of his needles into Reese’s ulnar nerve.
Stanton and Reese meet with two American agents, who know Stanton as the replacement for Miller, who failed at his job. As Stanton pours them bourbon, Reese tells them that he’s been sent to find Alim Assir, a terrorist who has escaped the country. The agents claim that the terrorist bribed Customs to get out, and Stanton accuses them of taking bribes. She then shoots them dead before they can react.
The Germans call Carter to complain about Reese, and she goes to the scene. Fusco calls Finch, who warns that Reese hasn’t checked in with him. Once he hangs up, Finch asks Anja to trust him.
When Reese doesn’t crack, Kohl explains that he was good at killing. The Stasi recruited him because of his expertise, and Kohl did whatever they asked to him for the good of his country. Reese admits that he was the same and warns that revenge won’t help him, but Kohl continues torturing him to find Anja.
Anja explains to Finch that her husband loved her, and took her with him when he had to flee when his teammates betrayed him. They traveled separately to the Soviet Union, but the Americans caught up to her and showed her photos of the people that Kohl had killed. Realizing what her husband was, Anja asked for and received asylum, and the Americans set up the fake car accident to make Kohl think she was dead.
When Reese still refuses to talk, Kohl searches Anja’s apartment and finds a photo of the daughter he never knew, Marie. He continues his search and finds a photo album with pictures of Marie, along with correspondence from Columbia University. Reese warns him that it’s too late for the two of them but that Marie can still have a normal life. As Kohl prepares to kill Reese to prevent him from following him. Fusco arrives and tries to capture Kohl. Kohl shoos back and escapes, and Fusco frees Reese.
Marie is leaving her class at Columbia and finally has a chance to check her phone. Before she can read the numerous missed messages from her mother, Kohl approaches her and takes her away at gunpoint. He has Marie call Anja and arrange for a meeting at the nearby park. As Kohl takes Marie there, he asks her if she knew her father. Marie explains that Anja told her that her father was a soldier and died a hero, helping his wife and unborn daughter escape after the fall of the Berlin Wall. She asks if he knew her father, and Kohl says that he did... once. They arrive at the rendezvous and find Anja and Finch for waiting for them. Reese comes up behind Kohl and orders him to surrender.
Carter gets an anonymous call that her shooter in a suit is at the park. She takes officers with her and finds Fusco there, and they start to search the park.
Anja tells Marie that she learned who her husband really was. Alone and trapped, with a child on the way, she had no other choice but to fake her death and leave him. Anja asks Kohl to forgive her for what she did, and Kohl says that he had to see both of them. He tells Anja that a part of him has always been there with her, and then prepares to shoot her. Reese tells him to stop but Kohl refuses, and Reese has no choice but to shoot him. As Finch gets Anja and Marie out, Kohl admits that she was right to fear him. Once they’re gone, Reese checks Kohl’s gun and confirms that it was unloaded. The dying Kohl says that he wouldn’t have shot Anja, and that he knew Reese would shoot because they’re both soldiers. Kohl says that his countrymen took everything from him except for the part that survived as Marie, and then passes away. Fusco and Carter arrive a few minutes later and find Kohl’s corpse, while Reese watches from the bushes.
Stanton tells Reese to get rid of the corpses and the murder weapons, and says that a reliable anonymous source informed her that the two men were traitors. Reese isn’t convinced and Stanton tells him that the threat is real and that his country needs him. As she goes, Stanton tells Reese to cut himself off from his old life completely because now he’s walking in the dark, and chooses his new name: “Reese.”
After Kohl’s funeral, Reese and Finch visit the man’s grave. The German authorities have covered up Kohl’s existence and are now pretending that he never existed. The two partners wonder if anyone will care about their names, and Reese figures that they’ll only matter after they’re dead.