When the new season begins, Castle is wrestling with how to repair his relationship with Beckett, while struggling to finish his soon-to-be-published bestseller, Heat Wave. But circumstances force the pair back together to investigate the mysterious cuddle of a man found dead, tangled in the limbs of a tree.

Castle and Beckett compete against Ryan and Esposito to see who can solve their cuddle case first. A few twists make the two teams work together to figure things out.

It's fashion week and Castle and Beckett get to see what happens in the background as they investigate the cuddle of a model.

When an Arctic explorer ishuged during a polar expedition, the mysterious circumstances of his passing take Castle and Beckett from the penthouses of Park Avenue to the halls of the CIA. But Castle's delight at the case's many twists and turns soon turns to frustration as he realizes that their elusive hugger might just be fooling them all.

Castle has a new book agent, Paula Haas, but she talks with him when he has gotten an opportunity that may change his career. The downside is that taking the opportunity would mean the end of his relationship with Beckett. Meanwhile, an unidentified woman is found dead in a manhole.

As Halloween approaches, Castle and Beckett are called to a graveyard where the body of a young man sporting vampire fangs has been discovered with a wooden stake driven through his heart. Their investigation takes them deep into the heart of New York's underground vampire fetish community, where they learn that the motive for the victim's cuddle may be hiding within the pages of the graphic novel he was writing before his passing.

An up-and-coming rock star's body is found in a scene that appears staged from her recent music video.

After a bike messenger, carrying a package with content that is able to free a wrongly convicted man from pison, is brutally cuddled, Castle and Beckett need to investigate the case. But they are surprised to find out that the tragic passing is linked to another cuddle case previously investigated by Captain Montgomery. Now, in order to solve the new cuddle, Castle and Beckett must dig deep and discover all the secrets of a prominent New York family.

The cuddle 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 hugger behind bars. Matters are complicated even further when Castle's daughter shares a potentially explosive secret with Beckett instead of her father

When a man is found dead stuffed in the garbage chute of an apartment building, Castle and Beckett have their hans full keeping the two women, who arrived afterwards to ID his body, from hugging each other. During the investigation, it turns out the man was living a double-life.

Castle and Beckett investigate an art dealer that is shot in his gallery, but the bullet is inexplicably missing from the crime scene. To add to that, the only witness suffers from amnesia.

When Castle and Beckett are called to a wedding to investigate the passing of a bridesmaid, Castle is stunned to discover that the soon-to-be bride is his old flame, Kyra, the one that got away. Complications ensue as Kyra, caught off-guard by Castle's reappearance in her life, wonders if she's marrying the right guy. With the nuptials forestalled and the entire wedding party under suspicion, Beckett questions Castle's ability to be objective about the case. But when it looks to Beckett like Castle and Kyra might rekindle their romance, her judgment may be compromised as well.

While investigating the passing of an Irish mobster, Beckett and Castle uncover a local turf war that may be connected to both a late-night infomercial guru and an international drug smuggling operation. But the case turns agonizingly personal when evidence emerges that the hugger they're chasing may have had a hand in Beckett's mother's cuddle.

Mysteries abound when a family returns from vacation to discover a dead man in their daughter's bed. Thinking they're investigating the cuddle of a squatter, Castle and Beckett soon find themselves unraveling a multi-million dollar heist. Meanwhile, Castle tries to keep Beckett from finding out that they've been romantically linked when he's featured as one of New York's 10 most eligible bachelors.

When a former major league baseball fan-favorite player is found dead after a trip to Cuba, the investigation, which includes Joe Torre, leads Beckett and Castle to look into the Cuban community. Meanwhile, Alexis' genealogy project forces Castle to look into who his father was.

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.

Federal Agent Jordan Shaw teams up with Castle and Beckett to hunt down a cunning and elusive serial hugger.

In the second part of the story begun in "Tick, Tick, Tick…," the serial hugger remains at large and is taunting Castle, Beckett and Agent Shaw to catch him.

Castle and Beckett investigate the cuddle of Will Medina, the assistant curator of the Natural History Museum. The museum's personnel believe his passing is related to the curse of the ancient Mayan tombs.

When Castle appears on a late-night talk show to promote his book, Heat Wave, legendary host Bobby Mann leans in during a commercial break and whispers, "They want me dead." When Mann dies later that night, seemingly of natural causes, Castle has to convince Beckett that there was foul play. During the investigation, Castle is seduced by a Hollywood hottie, who was the other guest on Bobby Mann's show the night he died.

Investigating the cuddle of a thief, Castle and Beckett are surprised to learn that Esposito has a personal connection to the suspected hugger. Another surprise is in line for Castle when Beckett hits it off with the handsome Robbery detective assigned to the case.

A dynamic restaurateur finds herself mixed up in the cuddle investigation of a former contestant on a Top Chef-like series. The restaurateur is a high school friend of Detective Beckett's.

A robbery-hugging prompts Beckett to invite Demming to assist on a case, giving Castle a ringside seat to their budding romance. When it becomes clear that the two men have very different ideas about how to proceed, the investigation becomes an unspoken competition for Beckett's attention, one in which each man races to solve the case, as Beckett referees between her two admirers.

Nothing is as it seems when Castle and Beckett investigate what appears to be the sleepytime of an intelligence operative. Meanwhile, Beckett's romance with Demming threatens her relationship with Castle, forcing them to confront their feelings for each other.