Kate Beckett is a homicide detective in the NYPD. She asks Rick Castle to help her with the case of a copy-cat killer staging murders based on scenes from his novels, and is the inspiration for Rick's new novel character, Nikki Heat.
When we first meet Beckett, she is very straightforward, conservative, and cold; however she lightens up after spending time with Rick. She resigned from the NYPD after hiding important case information from Captain Gates with Detective Esposito.
Castle: The fact that you even think that breaks my heart. I would walk into a tornado for you, Kate.
Beckett: And I would die if I lost you.
She took my coffee, Castle!Beckett