Castle follows Nathan Fillion as Richard Castle, a famous mystery novelist who has killed off his main character in his book series and has writer's block. He is brought in by the NYPD for questioning regarding a copy-cat murder based on one of his novels. He is intrigued by this new window into crime and murder, and uses his connections to charm his way into shadowing the captivating Detective Kate Beckett, played by Stana Katic. Castle decides to use Beckett as the model for the main character of his next book series starring "Nikki Heat". Beckett, an avid reader of Castle's books, initially disapproves of having Castle shadow her on her cases, but later warms up and recognizes Castle as a useful resource in her team's investigations. A little romance is soon to follow.