Original air date: 09/28/2015 Runtime: 43:03 min. After receiving a mysterious tip from her past, Beckett is launched into a fight for her life, with a team of mercenaries hot on her trail. As Castle investigates why his wife is on the run, Beckett must figure out who wants her dead, before they can finish the job.
Original air date: 10/05/2015 Runtime: 42:36 min. 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.
Original air date: 11/09/2015 Runtime: 42:54 min. Detective Slaughter returns to enlist Castle's help in solving a high-stakes robbery case. But when a body is found linked to the crime, Slaughter becomes the number one suspect in the heist turned murder, while Castle has to determine whether he's guilty or help to prove he's innocent.
Original air date: 02/14/2016 Runtime: 42:24 min. 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.
Original air date: 02/29/2016 Runtime: 42:59 min. Beckett and the 12th Precinct look into the murder of an English as a Second Language student. When the victim's class won't talk to the police, Castle goes undercover as a French Canadian immigrant and learns the victim was more than he seemed.
Original air date: 04/04/2016 Runtime: 43:02 min. A clue at the scene of the death of an armored-car driver leads Beckett and Castle back to an old case solved by Esposito. Complications arise when they learn Esposito might not have been telling them everything about his relationship with the culprit.