The FBI continues to track leads to the person who stole the deadly chemical. It is a race against time, since they need the antidote for Castle who has been infected with the chemical.

Esposito and Ryan investigate a former TV star's murder, but Beckett and her partner take over the case and do not want them, or Castle, involved.

A woman wakes to find her boyfriend murdered in her apartment. She eludes police and takes hostages and waits for Castle to help her. Castle believes she has been framed, and works with the team to prove her innocence.

The team investigates the ritual murder of a woman. Symbols on the woman's body and the items left in her apartment seem reminiscent of The Da Vinci Code. Alexis and Pi have moved to their own apartment. Castle finds it hard to accept.

Alexis volunteers in a criminal review organization to help prove a man was wrongly accused of murder 15 years ago. With his execution scheduled in three days, Alexis asks her father to bring a new look at the evidence.

A renowned relationship therapist is murdered. The team investigate a couple whose files are missing from the office, and find a perfect, priceless, 100 karat diamond is at the heart of the mystery.

When a woman who looks very similar to Lanie is murdered, the team thinks the killer may be targeting members of the 12th precinct.

A man dies inside a church, protecting a baby. The team has to find the guy's killer and the baby's parents. The man is connected to a crime, but by protecting the baby he does not fit a normal criminal character.

Castle and Beckett must find a serial arsonist as Ryan and Esposito struggle for their life in a building set on fire.

Castle and Beckett have to deal with the sudden appearance of Castle's father while solving the murder of a computer hacker who was working for the covert agent.

When a rising young pop star is found dead in an alley, Castle and Beckett delve into the victim's out-of-control hard-partying lifestyle, but as they dig deeper, a shocking revelation threatens to rock their investigation.

The murder of a PA at a top fashion magazine brings Castle and Beckett face to face with a tangled web of suspicion and corporate politics - and with the magazine's formidable editor, who still remembers Beckett's brief career as a model.

Castle and Beckett investigate the death of a mean high school girl at one of Castle's alma maters. Castle is thrilled when he discovers that it might be the work of a teenage telekinetic.

Castle and Beckett are baffled when a confused woman with an unshakable alibi gives a detailed and convincing confession to a murder. Then a second person walks into the precinct and makes the same confession. And then a third.

Investigating the killing of a Japanese ballerina, Castle and Beckett find a shrine with the murder weapon in an old factory. Then, when the two are separated, Castle is ambushed by a hooded attacker bearing all the hallmarks of a ninja.

Investigating the death of a Wall Street trader leads Castle and Beckett to discover that the victim was an undercover informant for the U.S. Attorney's office.

When construction workers uncover a mobster's body buried in concrete for 35 years, Castle and Beckett must try to talk to a fellow mafioso so stricken with grief that he lives as a recluse in a Seventies time-warp.

A promising professional skateboarder is killed by a motorcyclist, so Castle and Beckett dive into the world of extreme sports to investigate the murder.

A man Beckett has been secretly following is found dead - and then a notorious criminal involved in the first death is killed with Beckett's own gun. Faced with an elaborate frame-up, she has no choice but to run.

The wait is finally over for Castle as the wedding day approaches. Kate discovers that she's still married to her college sweetheart, and visits him to get a divorce. But he has problems of his own, bigger than anyone could imagine.