A nervous man named Jared Stone hops onto a subway train. Esposito lets Ryan know via phone that he’s followed the guy onto the car. Stone pulls a gun off a transit cop. He orders Espo to drop his weapon. We jump back three hours to see what led up to this dangerous turn of events.
Paul Reeves is found dead from a gunshot wound to the head in a park. The victim’s brother says he was an investigator for the Government Accountability Office where he took on some major players in the federal contract game. He got a phone call from an Occupy Wall Street activist/hacker before he was killed. The caller’s name: Jared Stone.
Ryan and Esposito head off to find Stone. They have a genuine conversation about each man’s future as a family man. Well, Ryan thought it was genuine until his partner cracked a joke about his biological clock. The detectives spot Stone. Esposito follows him onto the subway catching us up to present time. Esposito is forced to give up his gun. A hostage situation evolves.
Captain Gates orders the squad to find out why Jared Stone is doing this. The team has eyes on the situation via video. Esposito tells Officer Marisa Aragon, the transit cop, that she may need to back him up. Stone reveals that he’s wearing a suicide vest filled with explosives. He has his hand on a dead man’s switch. The team realizes that Jared Stone may be a terrorist.
Stone was on his way to attend a wealth management seminar when Esposito stopped him. He was going a place where he could cause maximum damage. Castle believes this guy was never a man of action. Something must have triggered him. Stone wants someone named Erin Wilson released from prison. She’s a fellow hacker. She’s also his soul mate.
The Hostage Rescue Team sends Esposito a message letting him know they are coming in. Stone is hip to the play. He finds the camera and shoots it out. Lanie asks to see the video playback. She realizes that Stone is sick with flu-like symptoms. This new info may have something to do with a case Paul Reeves was investigating. With help from Officer Aragon, Esposito takes down Stone and neutralizes the bomb threat. Unfortunately, no one can leave the subway car as they may have been exposed to a deadly virus.
Esposito and the others are transferred to an isolation unit in the hospital. The team believes Stone was trying to start an epidemic. He likely killed Paul Reeves when he found out the he stole a virus strain. Stone was in cahoots with someone using a code name of White Knight, who actually used him as a patsy for a master plan. Castle and Beckett realize that Paul Reeves was investigating a company that was plotting an epidemic. Paul’s colleague at the Government Accountability Office, Carol Jarvis, was the mastermind. She’s White Knight.
Esposito is given a clean bill of health. Officer Marisa Aragon lets him know that he was saying Lanie’s name during the takedown of Stone. She says that who you think of in a moment like that has weight. It means something. Guess that why Espo gives Lanie a big hug back at the precinct. Castle offers to celebrate this reunion of colleagues and friends by treating everyone to drinks at the Old Haunt. They can take the subway.