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.
Soft porn tycoon Beau Randolph was strangled with a bra during a grand party to launch another College Girls Gone Crazy franchise production. He received many death treats, such as from arch-conservative Ronald Armstrong's grim prudish movement. Beau's own bodyguard Scarlet Jones, whom Javier finds irresistible, stole a memory card from his safe and was hired by children's TV production firm. Actress Tiffany Shaw also lies a lot about her disguised party presence, which is only the top of an iceberg of family and business secrets.
A professional hit victim's corpse is found in a parking facility. The team works out she worked for US senator William H. Bracken, whom Becket holds responsible for her mother's murder, but seems to be the actual target. Only Castle learns that Becket hesitated whether to hold back evidence before another clue lead the team to prime suspect Robert McManus, a fired mechanic who blames the senator for his son's suicide. The senator is hell-bent on holding a high-profile speech in a hotel to launch a career-crucial environmental bill.
The corpse of Hannah Green, star of a fashion house reality show, is found in a Manhattan alley, but she has bruises from captivity elsewhere for the day she went missing from the studio. The team unravels complex rivalries for parts, infidelity and spin-offs, both a clothes line and Margo's son Stone Gower's series project with co-star Collette's daughter Ashley. Castle and Becket fear the captain will discover their affair after he accidentally drops her Valentine's present in the captain's coat
Saudi student Hasim Farouk, at Columbia like Alexis, is killed by a van crashing into him while he fired at it. The team soon works out the van was used to kidnap not only Egyptian tycoon Anwar El-Masri's daughter Sara, but also Alexis, whom she met at a lecture. FBI agent Harris's sole trace, obtained only because Becket 'turned away' from Castle slightly torturing the wounded van driver, runs dead. Meanwhile the girls attempt an escape, but discover the container they were held in now stands in Paris.
Anwar El-Masri pays $3,000,000 ransom for the kidnapped girls, but only his daughter Sara is released. FBI Agent Harris must wait days for red tape before the FBI and NYPD can actively search for Alexis in Paris, being out of jurisdiction. So Castle goes alone and hires through a friend shady problem solver Jacque Henri and his tech sidekick 'la taupe'. They find where the girls were held and arrange anther exchange. Castle is in for shocking surprises, first betrayal, then who saves him, from whom, and how to get Alexis back.
Castle is shaky after watching a DVD which predicts, in flashy amateur horror style, the exact time of death, for no apparent reason and probably by panic-caused cardiac arrest, of the murder victim, screaming in the phone, who received it. Her ex has a solid alibi and couldn't make sense of her panic about 'it'. Tracing the DVD's shipping leads to another copy recipient, killed at home similarly. Their only link is having been jurors on executed country serial killer Nigel Malloy's trial. The team heads for his home town, loved-ones and surviving jurors.
The corpse of Jimmy, a baker popular for cup cakes, is found in his industrial dough mixer. His apprentice Todd noticed, before being sent away, someone arrived in a rare collectors car, probably belonging to Irish mob lord Robert 'Bobby S.' Shannon's right hand, Liam Finch. After FBI agent Sam Walker tells Jimmy was his informant, Ryan astounds his team by revealing he has been undercover in that gang years ago and chooses to revive his alias Kevin.
Castle is home, mostly alone, in a wheelchair after a skiing accident, bored out of his wits just before his birthday. After a while, he actually picks up a pair of binoculars Alexis gave him to play Rear Window. Indeed, right across the street a foxy resident betrays her studly husband with a younger hottie. Shortly after, the cheated husband finds his rival's hat, wields a knife and seems to dispose of the corpse while she isn't seen again. Yet his NYPD team mates only reluctantly investigate and can't find any proof. Castle becomes obsessed with the possibility ...
Castle is jealous when Beckett has to protect a billionaire from an unknown killer. Castle wants to solve the case fast because it means Beckett will no longer have to be with the charming entrepreneur.
After tracking a killer to his apartment, Beckett steps on a bomb trigger and must stand in place while the bomb squad finds a way to defuse it. Castle stays with her, and they argue over who liked who first, via flashbacks.
When Homeland Security inexplicably seals the crime scene of a car bombing, Castle and Beckett find themselves with two mysteries on their hands: who murdered the victim, a government whistleblower, and why are federal agents trying to take over the case? The plot thickens when they discover that the victim wasn't killed by a car bomb but by a missile from a military drone.
The team investigates the death of a woman who hacked a law office for a specific file. It seems she thought her best friend was killed, and she was on a lead to that killer. Beckett interviews with the FBI.