Castle & Beckett confront the possibility of paranormal foul play when a world renown ghost hunter is mysteriously murdered while investigating a haunting at a legendary New York mansion.
When an astronaut training for a trip to Mars is mysteriously killed inside a Mars simulation, Castle and Beckett don spacesuits to investigate. But when they discover no one inside the sealed simulation could have committed the murder and no one from the outside could get in, the case takes a shocking turn.
When an ER physician is gunned down in the street, Castle and Beckett soon discover that the victim was a mob doctor to a Mafia family run by an old friend of Castle's. Also, against the backdrop of Christmas, Esposito and Lanie reach a defining moment in their relationship.
Detective Kevin Ryan is on the security detail of a charismatic congressman attending a charity event when shots suddenly ring out. Driven to apprehend the killer, Ryan must revisit the events that led up to the shooting, with the help of Castle and Beckett.
Castle and Beckett investigate the apparent robbery-homicide of a New York cab driver, only to discover that the victim was involved in a mysterious conspiracy with unimaginable consequences. As the stakes continue to rise, hard-charging federal agent Mark Fallon (guest star Adrian Pasdar) takes over the investigation. Together, Fallon, Beckett and Castle must race to unmask the truth about the victim before it's too late.
The murder of a high school mean girl draws Castle back to one of his many alma maters, where he is giddy to learn that the evidence points to a surprising perpetrator - a teenage telekinetic, throwing he and Beckett into a real-life "Carrie."
The murder of an Assistant District Attorney thrusts Castle and Beckett into the world of ex-cons and escorts. But when Castle's desire to help a vulnerable call girl endangers the case, Beckett is forced to decide between honoring promises and putting a killer behind bars. Matters are complicated even further when Castle's daughter shares a potentially explosive secret with Beckett instead of her father.
When a body is found in the theater of Martha's latest show, Castle and Beckett's investigation leads them into the unexpectedly dangerous world of competitive a capella.
When a half-naked woman is found covered in caramel sauce and hanging by bondage cuffs in a public park, Castle and Beckett's investigation takes them into New York's underground world of sexual domination. Naturally the case serves as sexy fodder for their already charged relationship banter.
In the first of a two-episode story arc, Castle & Beckett begin a murder investigation that also exposes a plot to kidnap the daughter of a wealthy Middle Eastern businessman.