'Castle' Season 7 Spoilers, Recap: 3XK Serial Killer Returns, Orchestrates a Kidnapping

In its most recent episode last Monday on ABC, "Castle" delved into the serial killer plotline, specifically the one centered on 3XK, aka Jerry Tyson (Michael Mosley), who returned along with his accomplice Dr. Nieman (Annie Wersching) and pulled off another kidnapping.

Titled "Resurrection," the episode started with the discovery of another dead body – that of a blonde woman who appeared to have been strangled after she apparently managed to escape from her captors. Lanie Parish (Tamala Jones) noticed that she had plastic surgery and resembled another woman, Pam, who was murdered previously. This clued the team into the possibility that they were hunting 3XK and the plastic surgeon Nieman.

However, in a subsequent interrogation Nieman denied any involvement with the women who had surgeries and with Tyson.

Mystery novelist Richard Castle (Nathan Fillion) joined the team to assist Detective Kate Beckett (Stana Katic) of the New York City Police Department as a consultant. They soon found a surveillance video of another woman who also looked like the dead woman from the alley, leaving apparently with Tyson in a car.

They discovered that the car belonged to Michael Boudreau. When they went to Boudreau's house, they were surprised to find "Tyson" who they quickly arrested. However, the man they apprehended claimed that he was actually Boudreau and that he had been duped into getting plastic surgery to look like Tyson. Subsequently it was revealed that he had Boudreau's fingerprints.

Nevertheless, the team brought Boudreau/Tyson to the precinct. To prove the man's real identity, Castle and Beckett tracked down Tyson's mother to get DNA samples. But they found out she was only Tyson's stepmother.

Luckily, the woman happened to keep Tyson's baby tooth and she gave it to the investigators. The team compared the tooth's DNA with that from the saliva found on a bottle in Boudreau's apartment, not knowing that the evidence was planted. When the test proved that the DNA did not match and that they had Boudreau, not Tyson, in custody, they ended up releasing him along with Nieman.

Meanwhile, Beckett tracked down Amy Barrett, the blonde woman last seen with Tyson. She initially refused to cooperate with Beckett as she claimed to be Tyson's girlfriend.

Then Beckett was suddenly kidnapped after being injected with a drug. Castle then realized that Tyson intended to be in the police precinct to get an alibi for what he was about to do. This will be known in the next episode.