Castle and Beckett must set aside their differences with Agent Fallon while trying to prevent a city-wide catastrophe.
While investigating an apparent robbery-homicide, Beckett and Castle discover the victim was involved in a mysterious conspiracy; as the stakes rise, a federal agent (Adrian Pasdar) takes over the case.
An old friend of Castle's emerges as the prime suspect in his wife's murder.
The murder of a lottery winner leaves Castle and Beckett with a wealth of suspects; Martha must decide what to do with her inheritance.
The retired lead detective on Beckett's mother's homicide case is gunned down after telling her he has new information; Castle and Beckett's partnership grows stronger.
The owner of a historic magic shop is found dead in Houdini's water torture tank; a new romance comes to light.
When Castle's novel Heat Wave becomes a movie, actress Natalie Rhodes accepts Beckett's invitation to visit and learn about the character she will play; Natalie observes Castle and Beckett's investigation of the murder of a matchmaker.
When a bar owner's body is found in the East River, the investigation takes Castle and Beckett through the forgotten tunnels and passageways of turn-of-the-century New York; Castle considers buying a bar.
When a prominent astrophysicist is found dead in her car, Castle is led to theorize her death was the result of an alien abduction.
While investigating a subway worker's murder in Central Park, Castle and Beckett unexpectedly uncover a boy's abduction.
When Beckett and Castle respond to an 'officer down' call, they discover the victim is actually a male stripper dressed as a cop.
When a beautiful woman is found dead, the evidence indicates a notorious serial killer known as The Triple Killer.
An unknown woman falls out of a casket along with the original deceased when pallbearers lose control of the casket at a funeral; the investigation takes Beckett and Castle into the world of amorous, bed-hopping physicians.
A young mathematician is shot with a 200-year-old bullet, inspiring wild theories by Castle about a time-traveling murderer.
When a coded document attracts Castle's attention, Beckett must steer the case back to the violent felons who populated their victim's world; when Beckett's ex-partner arrives, Castle must watch the relationship become romantic.
Beckett and Castle search for a psychic's killer while debating the existence of extrasensory abilities.
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