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.
When Beckett and her team burst into an apartment on a murderer's trail, they see Castle standing over a dead woman's body holding a gun; Beckett arrests Castle as he asserts his innocence.
Successful New York mystery author Richard 'Ricky' Castle get permission from the mayor, as a personal favor, to seek inspiration and factual documentation by tagging along with a detectives team.
Castle and Beckett investigate what seems to be an intelligence operative's assassination; Beckett's relationship with Demming strains her relationship with Castle.
A robbery-homicide prompts Beckett to invite Demming to assist on a case; the investigation becomes a competition for Beckett's attention.