Sex offender ex-con Tyler Faris is found in an alley, cut in half by a sword. Faris' victim claims that a man in a superhero uniform saved her. Even Castle doesn't recognize the uniform, which is eventually identified as Lone Vengeance, the hero of an Internet site authored by Sean Elt, a pseudonym. Actually, several people prance around New York in Lone Vengeance suits. The team investigates them and Tyler's enemies, such as his former employer Tony 'The Butcher' Valtini, thus proving to Captain Victoria Gates her lack of confidence in them is unwarranted.
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, and a sleazy porn mogul who invested in a modern-day "fountain of youth." Meanwhile, Alexis finds out whether she got into Stanford.
Student Jane Herzfeld was fatally shot with the Glock service pistol stolen from Detective Ryan by serial killer 3XK. Her ex-boyfriend, Finn McQueen, has an alibi. Phone records show she was in contact with undercover narcotics Detective Seth Carver. He had forced her to inform on Chinese mob boss Clifford Lee by acting as a tutor to his son, Ben. Castle ingeniously finds some missing links through prison records.
Atlantic City (New Jersey) hotel-casino co-owner Sam Seigel's corpse is found in an abandoned New York warehouse. Captain Victoria Gates keeps Becket in the office to test her skills 'without Castle's help'. The boys appreciate female absence as Ryan owes them a bachelor's party, but Javier's logical place as best man was already taken by the bride's teenage brother. Marino's partner Charlie Turner and his security expert Daniel Sullivan cooperative until the team gets close, linking the murder to the mob and employee Nadine Espinoza's disappearance. Turner throws the...
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 naming Best of Show at a dog show. Castle gets the Labrador he was training temporarily adopted as team mascot, and his nose proves quite useful. Airhead reality TV star Kay Cappuccio, seen leaving Pilar's room, 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 diary of a P.I from the 40's found in the effects of a murdered modern-day treasure hunter is the key to finding the Blue Butterfly, a blue-diamond necklace. The team works out the story situated in 1947 in the same, now derelict, music club, 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 recording of TV show "A Night of Dance", spoiled-rotten rich girl Odette Morton, who made it to the semi-final, is murdered in her easily accessible dressing room. Suspects include a previously knocked-out candidate who is now automatically restored, the presenter and someone he had a secret with. But evidence shows Odette's has a big secret of her own that she recently 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 Captain Gates to help out by using his speed-reading ability and attention to detail to sifting through mountains of witness depositions. This helps the 12th precinct team get on the right track after the FBI concentrates on 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 Beckett. 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 Beckett commits...