Cop killer Hal Lockwood, whom Becket visited unsuccessfully in jail for months hoping for a lead in her mother Johanna's closed murder case, is released by a faked order into the general population, where he slices fellow rogue cop Gary McCallister's throat, then is helped by fake cops to escape. Becket, his likely next target, receives warnings from her father, Montgomery and Castle. Much helped by Ryan and Esposito, the duo work out there must be a police accomplice and/or mastermind controlling Chuck Ryker, the debt-ridden corrupt jailer who was found murdered.

Castle is grieved when Becket, once regaining health, tells him to leave her time without calling for months. Yet when she returns to work after therapy, Ryan and Esposito tell Castle help them keep the case of her mothers killers going, behind ex-IA by-the-book-Captain Victoria Gates's back. They work out the only remaining angle are bank files lost in a fire, according to decorated officer Rod Halstead definitely no arson. Becket grudgingly passes her gun exam, but can't perform in real danger anymore in their assigned case, the ingeniously staged murder of a rock ...

Sex offense ex-con Tyler Faris's corpse is found on the street. He was cut in half by sword, in front of a former victim, by a man in superhero uniform, which even Castle didn't recognize as Lonely Vengeance, the hero of an Internet site authored by Sean Etel, a pseudonym. Actually, several people prance around New York in Lonely suits. The team investigates them and Tyler's enemies, such as his former employer Tony 'The Butcher' Valtini, thus proving new captain Victoria Gates's lack of confidence in them unwarranted.

A medical researcher's body has disappeared from the street where he was fatally shot. Actually the van which collected him thus fulfilled a cryogenics contract, triggered by a death alarm. retrieving the bullet would 'kill' the corpse, so a compromise is struck: the severed head remains frozen. That proves the wrong choice, while possible motives are sifted true in the man's complicated personal, medical and scientific life and the project's funding motivation before another crime occurs.

Student Jane Herzfeld was fatally shot with the Glock service revolver serial killer 3XK stole from Ryan. Her only dodgy ex, Finn McQueen, has an alibi. Phone records show she was in contact with undercover narcotics detective Seth Carver, who forced her to inform on tutoring pupil Ben Lee's dad Clifford's Chinese drug mob. Castle ingeniously finds some missing links trough prison records.

Museum director Hayes is murdered at a special exhibition from which the diamonds-covered, $50,000,000 show-stopper 'Fist of capitalism' is missing. Suspects include the owners, the haughty McHugh couple, discretely fighting over a divorce, insurance investigator Serena Kaye, presumably a never caught 'former' master thief, and Falco, a British master thief presumably hired by Hayes, who was in dire debt. Serena is key to some dirty tricks.

National TV ghost-buster Jack Sinclair is killed on camera while investigating the famous New York McClellan house, site of 8 previous 'suspicious' murders. His cameraman Barry Bavetta resigned after a fight that day but has an alibi. Becket and Espinosa being skeptics, Castle mainly teams up with Ryan. The root of Sinclair's fear for the house and its very architecture prove key to discovering both another older murder and a list of present suspects, enabling to set a fitting trap.

Accompanying Martha to the bank, where she pigheadedly refuses his financial help, Castle's speculations over the phone with Becket that surgical mask-equipped customers may be robbers proves correct when everyone is held at gun-point. The call makes Becket the inexperienced hostage negotiator. Castle works out and manages to communicate both crucial and puzzling information. The hostage-chapter ends spectacularly abruptly, only to launch a very different hunt for the brain, who wasn't after cash at all.

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...

Shortly after a kindergarten teacher about to marry, a lawyer is expertly sniper-killed on a Manhattan street, without apparent link. Esposito's sharp-shooter training proves handy for the case and to help Becket deal with the rekindled trauma of her near-fatal shooting. Castle and his daughter's art course work out the only clues left at the distant sniper hideouts, cuttings from Renaissance paintings, each alluding to the next murder site. After a third target survives, Castle works out a superficial point in common and postulates a tragic motive.

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? Meanwhile, Ryan, Esposito and Gates are left to investigate their disappearance in a case where all is not what it seems.

A man's naked corpse seems to have fallen to his death, but a toxin killed him first. The modestly payed company employee turns out to be a serial seducer, who mysteriously deviated from his usual MO to pretend being a rich man. While disease grows over groom Ryan's future, Castle comes up with alternative, business-related motives and suspects on top of many scorned women.

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 ...

CIA agent Sophia Turner sidetracks the sleuths, but only to throw off Becket, welcoming Castle's input. Thomas Gage however reappears, is caught, escapes and convinces Castle of his innocence. The NYPD team finds out there must by a CIA traitor and tries at all cost to prevent the apocalyptic plan being launched by kidnapping a girl, painstakingly identified as the daughter of a very influential Chinese tycoon and party king-maker. Thereafter, Castle must deal with the cleverly elusive traitor.

One by one, successful career women, in party costumes from the same shop, are poisoned and staged murdered in ways, to fit the Grimm fairy tail characters of Red Riding Hood, Snow White and Sleeping Beauty, except that the last survives. They also each withdrew the same cash amount, apparently blackmailed for a hit-and-run they committed as college mates.

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 then leg work after a bomb explodes during an anti-globalist demonstration. Castle is asked by the captain as sharp observer. Sifting trough mountains of witness depositions, he sets their own team o the right track after the FBI arrests the wrong suspect.

A devilishly handsome detective from Scotland Yard, Simon Hunt, 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 Winthrop, 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 Becker, 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. Allthough 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, ...

Castle and Beckett investigate the murder of a man covered in human bite marks apparently caused by a Zombie attack.

When the murder of an Army veteran puts Beckett on the trail of the man who shot her, Castle must decide how much he's willing to sacrifice to keep her safe. As secrets are revealed and feelings are put on the table, the lives of the detectives at the 12th Precinct may never be the same.