ABC's "Castle" is about a mystery writer, Richard Castle, who is drawn into the world of homicide investigation. Castle partners with NYPD detectives Kate Beckett, Javier Esposito and Kevin Ryan to investigate murders, and his unorthodox ideas are often just what the team needs to solve the case.
In the pilot, Richard Castle is at a dead end after killing off the main character of his most successful series. When a serial killer begins staging murders based on his works, he consults with the NYPD to track down the culprit. Not only is he successful, but he also finds new inspiration in Detective Beckett, basing a new main character on her and securing a regular spot on the team. Castle uses his creative impulses, his high-society connections, and his freedom as a civilian to approach cases in ways the police detectives cannot.
"Castle" is a police procedural, with most episodes containing a single self-contained mystery. Over the course of the investigation, the team usually goes through several suspects, and Castle typically offers outlandish theories about the most unexplainable cases. Some recurring story arcs concern the murder of Detective Beckett's mother, the disappearance of Richard Castle's father, the growing romance between Castle and Beckett, and a serial killer known as "3XK" who targets the team on multiple occasions.