Richard Castle (Fillion) is a famous mystery novelist who has killed off the main character (Derek Storm) in his popular book series and has writer's block. He is brought in by the NYPD for questioning regarding two copy-cat murders based on two of his novels. He is intrigued by this new window into crime and murder, and uses his connection with the mayor to charm his way into shadowing Detective Kate Beckett (Katic). Castle decides to use Beckett as his muse for Nikki Heat, the main character of his next book series. Beckett, an avid reader of Castle's books, initially disapproves of having Castle shadow her work, but later warms up and recognizes Castle as a useful resource in her team's investigations.
