When a Lothario is killed, Castle and Beckett suspect that the victim's mysterious double life holds the key to his murder. Their investigation leads to a shocking twist that threatens to disrupt Ryan's wedding with Jenny.
When a woman is found murdered in her car, Beckett and her team's investigation leads them directly to City Hall... specifically to the Mayor, Robert Weldon, who happens to be a friend of Castle's, which could also jeopardize Castle's continued involvement with the NYPD.
Dog trainer Francisco Pilar is murdered after a disputed ruling in the Manhattan dog show. Castle gets the Labrador he was training adopted as team mascot till further notice, and his nosy proves quite useful. Airhead reality TV star Kay Cappuccio, the last seen in Pilar's tent, has a motive, but was he or she spied on by the camera planted in the dog's collar and why is there a customs undercover agent?
Castle senses a detective mystery manuscript found in the effects of a murdered modern-day treasure hunter is the key trough the jewel at stake, a blue diamonds-composed blue butterfly necklace. As the team works out the story situated in 1947 in the same now derelict music club, then Mahattan's place to be, involving murder, gangsters and theft, they work out the true parts and identities of culprits and victims.
The team's reputation is dented when Thomas Gage, a ruthless murderer whose identity proves totally faked, not only acts smug when arrested, but manages, as cryptically predicted, to escape and steal all evidence plus sensitive data from the NYPD computer. He's not only ahead of Castle and Becket to commit another murder, they are both abducted to a secret, deep CIA HQ, where Castle reconnects with Sophia Turner and their classified espionage past. The three team up and discover it's all about brilliant mathematical scientist Nelson Blakely, whose death was staged ...
During Charles Carson's TV knockout show "A Night of Dance", spoiled-rotten rich girl Odette Morton, who made it to the semi-final, is murdered in her easily accessible lodge. Suspects include a previously knocked-out candidate who is now automatically restored, the presenter and someone he had a secret with. But forensic evidence shows Odette's very true identity was a big secret shared with some people from her past, which includes another murder.
The FBI commandeers the NYPD detectives for little more than leg work after a bomb explodes during an anti-globalist demonstration. Castle is asked by the captain as sharp observer. Sifting through mountains of witness depositions, he sets the 12th precinct team on the right track after the FBI arrests the wrong suspect.
A devilishly handsome detective from Scotland Yard teams up with Castle and Beckett to find the person responsible for the murder of his friend's daughter. Also, Castle and Beckett suspect Nigel, the Deputy General at the British Consulate, 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.
Castle finally gets Beckett, who admits so only in therapy, she may have made him wait too long when he teams up for an investigation with her colorful colleague detective inspector Ethan Slaughter, a cowboy style bulldog, who was assigned multiple decapitated Jamaican corpses from the Irish Westies gang member Brian Reilly's maverick son. Although uncomfortable with the ruffian style, gentleman sleuth Castle proves his value while they discard a simple gang war and focus on newcomer Cesar Vales's Mexican gang. Castle not only repeatedly appeals to his former team, ...
The murder of a Latino army veteran ex-con, ex-Lobos-street gang member quickly links to a break-in in the late captain's home, to steal only and all his old police files, and yields the fingerprints of the sniper who nearly killed Becket. Castle realizes continuing the investigation will draw him back and probably cost her life by squashing his deal with deep throat. Her refusal to back down causes a break up with Castle, and Gates suspends both her and Esposito for continuing an unauthorized investigation in a case assigned to another NYPD team. Now Becket commits ...
Wendy Dupree, murdered in a cheap motel, wrote a clue in her blood. When Castle realizes it's no word but a number, it leads, in combination with her phone records, to a storage compartment, about to be auctioned, rented by her brother Wendell, an ex-con, who died in a suspicious accident a few months earlier. He was employed as driver by socialite Anjelica Henley, who recently reported a super-valuable diamond, stolen in a robbery, focus of further criminal intrigues. The earlier past provides the crucial clues, while Castle and his mother worry about Alexis's ...
After insurance broker Lloyd Kurtzman's employee Tessa is murdered at home, evidence piles up, all pointing at Castle, who denies knowing her, let alone having had an affair. Although none of the team can believe him guilty, they must arrest the sole suspect. Only then, vindictive serial killer Jerry Tyson manifests himself, promising Castle won't survive jail, which call for a radical solution.
During the annual major SciFfi convention, Nebula 9 - super-fan Audrey O'Neill, who finally organized with a nerd couple a life performance there starring the short-lived series' original cast as well after decade of 'webipsodes', is found dead on set, killed with a real 'space laser', of which only two working ones were custom-made. Castle, who has better taste, is amused to find Becket was part of a college fan gang. The team works out various personal, career and business motives as well as opportunities for cast and crew.
A rock band finally reaches fame, but one of its members, James Swan is found murdered in his trailer. Due to the inevitably high media profile, the city orders full cooperation with a TV crew which was already filming the band in reality-style. That makes Javier show off, Kate camera shy, while Castle pulls the strings, almost like a director. The team finds conflicts within the band. Roadie Hank Rodgers also proves a link to John Campbell, from whose abusive cult Swan escaped and whom he recently met and paid a small fortune cash.
When Beckett & Castle pick up a witness to a murder, hired killers attack, and they lose their cell phones and Beckett's gun. They run for protection while Esposito and Ryan try to find them. The killer is not who they suspect.