Castle Esposito (Jon Huertas, left) was on a subway train taken hostage by activist Jared Stone (Will Rothhaar, right) in episode 8 of "Castle" Season 7. Photo: ABC

“Castle” returned Monday night to modernity after an Old West honeymoon for Rick (Nathan Fillion) and Beckett (Stena Kati). However, episode 8, “Kill Switch,” would test the newlyweds with one of their most dangerous cases yet in Season 7 of the ABC series.

The episode began with the two arriving at their first crime scene as a married couple. Although the murder at first appeared to be a mugging, Beckett quickly deduced that it was premeditated crime. As they investigated the crime they discovered that the victim, a government investigator named Paul Reeves, may have been involved in a larger conspiracy.

Beckett found evidence that an Occupy Wall Street activist and computer hacker, Jared Stone (Will Rothhaar), was tied to the victim. Castle believed that Stone was a whistleblower who had given information to the victim that got him killed. Beckett sends Esposito (Jon Huertas) to find and bring in Stone.

Esposito followed Stone onto a subway car, but when he confronted him the hacker grabbed a bystander cop’s gun and took the subway car hostage, pulling the alarm to stop the train in its place.

Stone became paranoid after finding out that Esposito had been on the phone with a cop, his partner Ryan (Seamus Dever), and the authorities were aware of the situation. Luckily, Esposito had an ally in the other cop, Tory Ellis (Maya Stojan), even if she was unarmed.

Back at the station, Beckett had to console Lanie (Tamala Jones), who was worried about her on-again-off-again boyfriend. Then, Beckett was alerted to a security cam that had eyes in the subway car. They watched as Esposito tried to talk Stone down, but things got complicated when Stone revealed he had a bomb under his coat. Stone squeezed a dead man’s trigger in his hand, meaning if he let go the bomb would go off.

After seeing the bomb, Beckett and the police worked on finding out Stone’s original intentions and figure out that he was no whistleblower and had planned on attending a seminar of wealthy investors to blow himself up inside.

A police negotiator finally called Stone in the subway car and asked if the terrorist had any demands, but he only had one – to free Erin Wilson from prison. Beckett discovered that Wilson was a former hacker partner of Stone’s who took the fall for one of their schemes. However, Wilson had no knowledge of his plan so Beckett set to looking for other accomplices and discovered an organization called White Knight that Stone had mentioned on the train.

Back on the subway car, the police sent pizza for the hostages, including one with a special message for Esposito that when the tunnel lights flicker a hostage rescue team will try to enter the car. The message asked him to grab Stone’s hand when the raid began and hold it on the bomb trigger to prevent him from detonating it. However, Stone heard the rescue team on the roof and after calling the negotiator to demand for them to be pulled back he noticed the camera that had been on him and shot it out with his gun. With the police in the blind, Esposito made a move anyway and with the help of the other cop on the train he was able to stop and disarm Stone, but they were not out of trouble yet.

Ryan, who had gone to investigate Stone’s apartment, found a script for Stone’s actions that indicated that the whole hostage situation was a ploy to stall for time. Beckett and Castle dug through cases that the original victim, a reporter, was working on when he was killed. They came across a case where someone had stolen a deadly strain of the flu virus from the CDC to deploy as a chemical weapon. Stone had been showing signs of sickness the whole time.

The police took all the hostages into medical care and all were determined to be healthy except Stone. However, when Beckett and Castle questioned Stone they realized he had no plans to use the virus and had been intentionally infected by the White Knight, another hacker, as part of a bigger plan.

Beckett and Castle found a pharmaceutical executive (Wendy Braun) who had written emails to Stone under the alias as the White Knight. She had conspired to spread the disease to profit off its vaccine and used Stone as a patsy.

With the situation finally resolved Esposito returned to the station where everyone was happy to see him, Lanie most of all. The other cop on the subway train had pointed out to Esposito that he had mouthed her name (she could read lips) before making his move on Stone. Perhaps he and Lanie will finally come to their senses and get together.

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