When Castle and Beckett wake up in bed, handcuffed together, in a locked room with no memory of how they got there, they must piece together the mystery of where they are and why, all while trying to escape. But as the two of them adjust to being shackled together, what's the biggest threat they face... the people who abducted them or each other? Meanwhile, Ryan, Esposito and Gates are left to investigate their disappearance in a case where all is not what it seems.
When a bomb explodes at a protest rally killing five people, Castle & Beckett realize the key to solving the case is to reconstruct the 47 seconds prior to the explosion. Using video and witness accounts, they uncover the shocking truth about who planted the bomb.
A witness to a murder claims that he and the victim were attacked by a zombie. Castle and Beckett take a step forward in their relationship, with Beckett stating that "Her wall" is about to come down.
When a famous dog trainer is killed, the investigation keeps coming back to charismatic reality TV star Kay Cappuccio (guest star Hilarie Burton, "White Collar"). Kay, a favorite of tabloids and gossip websites the world over, has achieved stardom without possessing any discernible skill or talent. But there seems to be more to her story than she is letting on.
In a riveting opening that picks up just moments after last season's climactic finale, Detective Beckett (Stana Katic) fights for her life as Castle (Nathan Fillion), plagued by guilt over his role in the events, struggles to uncover who's behind her brutal shooting. Meanwhile, back at the precinct, Ryan (Seamus Dever) and Esposito (John Huertas) have to adjust, as Victoria "Iron" Gates (Penny Johnson Jerald, "24") becomes the precinct's new uncompromising Captain.
A devilishly handsome detective from Scotland Yard, Simon Hunt (Brett Tucker, "Off the Map," "Spartacus," guest stars), teams up with Castle & Beckett to find the person responsible for the murder of his friend's daughter. Also, Charles Shaughnessy ("Days of Our Lives") plays Nigel Winthrop, the Deputy General at the British Consulate whom Castle & Beckett suspect is up to more than just ambassadorial balls and diplomatic luncheons. Meanwhile, Lanie convinces Beckett that she needs to make a move on Castle before it is too late.
When Castle and Beckett investigate the killing of a treasure hunter, they discover the case is linked to a mysterious homicide from 1947 involving a hard-boiled private detective. Castle realizes the only way to solve the present-day murder is to solve the murder from the past. The 1947 case comes to life through stylized flashbacks, featuring Castle as the private eye and Beckett as a femme fatale
While investigating the mysterious shooting death of a young woman, Castle and Beckett face a cop's worst nightmare when they discover that the gun used in the killing is Det. Ryan's old service weapon - the one that was stolen by the serial killer, 3XK. Now with the clock ticking, the team must work to solve the murder, track down 3XK and retrieve Ryan's gun before the killer strikes again.
Gunshots, a fleeing van and a massive blood pool all point to murder, but when Castle & Beckett arrive at the crime scene, they discover that it lacks something - the victim! The investigation leads to the cutting-edge world of life-extension science, a cunning high-tech researcher (guest star William Atherton), and a sleazy porn mogul who invested in a modern-day “fountain of youth.” Meanwhile, Alexis finds out whether she got into Stanford.
When the murder of an Army veteran puts Beckett on the trail of the man who shot her, Castle must decide how much he's willing to sacrifice to keep her safe. As secrets are revealed and feelings are put on the table, the lives of the detectives at the 12th Precinct may never be the same.