Beckett receives a mysterious tip and is launched into a fight for her life with mercenaries on her tale; Castle tries to determine why his wife is on the run.
Castle and Beckett investigate the murder of a cruise ship entertainer, only to find themselves trapped at sea with the killer.
Castle goes to Los Angeles in hopes of finding answers about the time he can't remember, but ends up in danger when he is recruited by the Greatest Detective Society.
After Hayley does a favor for an old friend, she finds herself implicated in a killing and cyber-terror attack. Now, Beckett and Castle must rush to solve the case and clear Hayley’s name.
Castle thinks the Antichrist maybe involved in the death of an axe wielding psychiatric inmate who drops dead in the P.I. office.
When the body of a local college fraternity student is found gruesomely murdered, Castle has to go undercover as a professor in order to gain access to the victim's world. However, he and Beckett soon discover that behind the fun and games of college are some darker secrets the university wants to keep hidden.
Castle finally gets his day in court when he takes the stand as the key witness to a murder from five months ago. But when new information suddenly arises, he and Beckett must race against the clock to prevent a miscarriage of justice.
When a mild mannered safety inspector for the city (guest star Jonathan Silverman) miraculously survives a poisoning, it might be luck; but when he survives another, it’s a mystery Castle and Beckett will have to solve.
When a movie star turn stage actor is mysteriously killed, Castle and Beckett go backstage and discover he had more than his lines to worry about.
With their best lead in hand, Castle and Beckett are ready to take on LokSat. But an unforeseen twist puts their case – and their lives – in jeopardy.