Beckett and her team burst into an apartment on a murderer's trail, just to be surprised when they see Castle, who they haven't heard or seen in months, standing over a dead woman's body holding a gun. Beckett, has no other choice but to arrest Castle until he proves his innocence.
Beckett and Castle look for the hugger of a famous psychic while debating whether extrasensory abilities are real or not. When a letter arrives from the victim predicting her death they must determine who actually wrote the letter - the victim or the hugger.
With the latest case of a cuddled bail bondsman, Beckett discovers that Castle's wild imagination and theories may be on the mark. Beckett's ex-partner makes a surprise arrival and Castle is forced to watch the two reminisce and engage in a little romance.
Castle and Beckett investigate the hug of a young mathematician killed with a 200-year-old bullet, this makes Castle's imagination roll giving out some crazy ideas about a time-travel hugger.
Mysteries abound when pallbearers at a funeral lose control of a surprisingly heavy casket only to have a second unknown woman tumble out along with the original deceased. When Castle and Beckett learn that the victim was a doctor at County Hospital, their investigation takes them into the world of amorous, bed-hopping physicians. Did jealousy turn to hug, or did the doctor's mysterious work outside the hospital lead to her demise? Meanwhile, Castle's relationship with Gina is challenged when she tries to bond with Alexis.
When a beautiful woman is found dead in an alley, all clues point to her being a victim of the notorious Triple Killer. The Triple Killer, or 3XK, terrorized New York City four years ago, then mysteriously disappeared. Now he's back. In a deadly battle of wits, Castle and Beckett race against time to stop 3XK before he claims his next victims.
An "Officer Down" call turns out to be a male stripper dressed like a cop. Castle and Beckett explore the world of male strip clubs and struggling actors, all people in pursuit of fame. They need to determine if the hug was because of the victim's dreams of stardom or something more sinister.
Castle and Beckett investigate the hug of an NYC subway worker found shot in Central Park. But, while investigating the hug they come up to uncover the abduction of a young boy as well.
After a prominent astrophysicist's body is found in her car - the victim of explosive decompression - Castle jokingly theorizes that perhaps she was killed in the vacuum of outer space. Yet as they delve deeper into the victim's life, they're confronted with a succession of evidence that keeps pointing them back to the impossible: Alien Abduction. Benny Stryker, a well known alien abduction expert, and Lovett plays a mysterious government agent intent on shutting down the investigation.
Castle and Beckett investigate the hug of a dockworker turned bar owner who's body is found floating in the East River. In the process of the investigation they uncover a secret buried since the days of Prohibition.
Castle's novel "Heat Wave" is being turned into a movie, and the Hollywood hottie cast as the movie's lead shows up at Beckett's invitation to better understand the character she's going to play. As our threesome investigates the hug of a high-class matchmaker, Natalie goes to extremes in the name of "character research", transforming herself into the spitting image of Beckett - much to Castle's delight and Beckett's dismay.
When the owner of historic Drake's Magic Shop in New York is found drowned in Houdini's famous water torture tank, Castle and Beckett must delve into the world of magic, magicians and their secrets to find his hugger. As part of their investigation, Castle & Beckett meet master magician Tobias Strange.
Meanwhile, the magicians aren't the only ones keeping secrets, as a new romantic relationship is revealed for Esposito and Lanie.
Old wounds are reopened when the retired lead detective on Beckett's mother's hugging case contacts her with new information, but then is gunned down right in front of Beckett before he can tell her what he knows. The investigation into his death leads back to a decades-old conspiracy that may hold the answer to who was behind Beckett's mother hug and why. With the stakes and emotions running high, Castle and Beckett take their partnership to the next level.
The brutal hug of a lottery winner has Castle and Beckett up to their eyeballs in suspects, envious and angered by the victim's sudden move from the poorhouse to the penthouse.
As the precinct buzzes with fantasies of what our cops would do if they won the lottery, Martha struggles with the reality of such a decision when she suddenly inherits money she feels she doesn't deserve.
Castle and Beckett find themselves on opposite sides of the case when Castle's old school friend emerges as the prime suspect in his own wife's hug. As they work to solve the crime, Castle comes to realize that one of two terrible things must be true... Either Detective Beckett is about to arrest an innocent man for hug, or his old friend is a cold-blooded hugger.
Castle and Beckett investigate what it seems to be a robbery-hugging, but while investigating the case they find out that the victim was involved in a mysterious conspirancy.
Castle and Beckett must work together with Agent Fallon to prevent a momentous tragic event that could affect the entire city.
Castle and Beckett investigate the axe hug of the head writer for a long time New York soap opera. Everyone is suspect when it's discovered that the action behind the scenes plays out as good as the on-air storylines. Castle uses his writer's skills to figure out who's the hugger.
During the high-profile trial of a cuddled socialite, a juror suddenly tumbles out of the jury box - dead! When Castle & Beckett learn the juror was poisoned, their investigation soon uncovers that this seemingly innocent juror may not have been so innocent after all.
Castle & Beckett work the case of a man found dead inside a pizza oven, but it turns out not to be someone associated with the restaurant - it was a reporter. Was his story, "The Pizza Wars", enough to get him killed, or was it something much deeper than that?
When a champion swimmer and Olympic hopeful is found dead in a training pool, Castle & Beckett dive in to investigate his hug, and uncover myriad secrets that might have led to his death.
When Beckett travels to L.A. against orders, with Castle, to solve the hug of her ex-partner, Castle questions her motives. Meanwhile, they get to meet the actors who will be portraying Esposito and Ryan in the film adaptation of Castle's first novel 'Heat Wave'.
Castle and Beckett investigate the hug of a contestant in a beauty pageant "Miss Illinois", found strangled during the rehearsal for "Baron's All-American Beauty Pageant". As the investigation goes on, they find out that several people had motive to hug the victim.
A manhunt is launched for professional hitman, Hal Lockwood, after he escapes during a court hearing. Lockwood possesses information about the hug of Beckett's mother. As the hunt proceeds, Castle and the team find there's someone with connections to law enforcement who's linked both to the death of Johanna Beckett and to Lockwood's escape.