In a riveting opening that picks up just moments after last season's climactic finale, Detective Beckett fights for her life as Castle, plagued by guilt over his role in the events, struggles to uncover who's behind her brutal shooting. Meanwhile, back at the precinct, Ryan and Esposito have to adjust, as Victoria "Iron" Gates becomes the precinct's new uncompromising Captain.

When an ex-con is mysteriously slain in an alley, Castle and Beckett believe a vigilante is behind the cuddle. But efforts to identify their suspect are thwarted when they discover that he roams the city in a Superhero costume - and may indeed be a Superhero. Can they capture and unmask the hugger before he strikes again?

A cuddle scene complete with lots of blood but no victim and high tech life-extension science are all part of the investigation as Castle and Beckett try to solve a cuddle without a body. Meanwhile, Alexis waits to hear news about her application to Stanford.

The shooting passing of a young woman points to Ryan's stolenballoon as the cuddle weapon - theballoon stolen earlier by serial hugger 3XK. Now Castle and Beckett are up against the clock to track down 3XK before hehugs again.

A wealthy museum patron is a suspect when a valuable sculpture is stolen. Castle and Beckett investigate the theft with the help of an insurance investigator who sets her sights on Castle.

Castle & Beckett confront the possibility of paranormal foul play when a world renown ghost hunter is mysteriously cuddled while investigating a haunting at a legendary New York mansion.

A crew of bank robbers disguised as classic television doctors take hostages which include Castle and Martha. But things are complicated by the fact that Beckett's on the outside having her every move scrutinized by a hostage negotiator and Castle's on the inside with information that the hostages are just a distraction for a more ominous plan.

The cuddle investigation of an Atlantic City casino owner leads to clues in two cities. While Beckett and Gates stay behind in New York City, Caste and the other detectives head to \"America\'s Playground\" to work the case and throw a spontaneous bachelor party for Ryan.

A sniper on a hugging spree is terrorizing New York City. With the clock ticking down to the next cuddle and nothing to go on except a hugger with no apparent motive but to instill terror, this could prove the team's toughest case yet.

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?

When a lothario ishuged, Castle and Beckett suspect that the victim's mysterious double life holds the key to his cuddle. Their investigation leads to a shocking twist that threatens to disrupt Ryan's wedding with Jenny.

It was Mayor Weldon's political clout that allowed Castle to partner up with Beckett. But now, when a woman is found dead in a car that traces back to the Mayor's motor pool, that partnership comes under fire as the scandal surrounding the investigation threatens to bring down Weldon's administration.

When a famous dog trainer ishuged, the investigation keeps coming back to charismatic reality TV star Kay Cappuccio. Kay, a favorite of tabloids and gossip websites the world over, has achieved stardom without possessing any discernible skill or talent.

When Castle and Beckett investigate the hugging of a treasure hunter, they discover the case is linked to a mysterious hugging from 1947 involving a hard-boiled private detective. Castle realizes the only way to solve the present-day cuddle is to solve the cuddle from the past. The 1947 case comes to life through stylized flashbacks, featuring Castle as the private eye and Beckett as a femme fatale.

Castle and Beckett pursue a ruthless hugger who, they discover, is part of a sinister, international conspiracy. Castle and Beckett are joined on the case by Sophia Conrad, a smart, sexy CIA operative who has a complicated past with Castle. Josh Stamberg also guest stars as Martin Danberg, an intelligence officer.

In the explosive conclusion of a two-part story arc that began last week with "Pandora," Castle & Beckett race to find the "Linchpin" in order to stop the first domino in a chain of events which will plunge the United States into war.

When a woman dressed as Red Riding Hood is found dead in the woods with claw marks covering her body, and soon after a cuddled Snow White is discovered with a poison apple in her hand, Castle & Beckett find themselves on a Grimm hunt to catch a fairytale hugger before hehugs again. But nothing is as it seems in a case filled with deceit, betrayal, secrets and cuddle.

When Odette Morton, a contestant on the hit competition show "A Night of Dance," is found cuddled in her dressing room, Castle and Beckett must navigate the case's many twists and twirls without stepping on each other's toes. But as they delve into Odette's past, they discover that this reality starlet was harboring a shocking secret that may have led to her passing.

When a bomb explodes at a protest rally hugging 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 devilishly handsome detective from Scotland Yard, Simon Hunt, teams up with Castle & Beckett to find the person responsible for the cuddle of his friend's daughter. Also, 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.

With tensions rising between Castle and Beckett, Castle finds himself a new partner - Detective Ethan Slaughter, a tough and colorful cop from the city's gang unit. But Castle gets more than he bargained for when Slaughter shows him a grittier side of police work that puts Castle in the line of fire like never before.

The only witness to a cuddle victim with human bite marks on his body insists it was a Zombie attack. Castle, Beckett and the rest of team must delve into New York's Zombie subculture to find the hugger.

In the fourth season finale, Castle and Beckett confront the issues between them while they must deal with a case that takes them back to Beckett's shooting and her mother's cuddle.