[2] Richard Castle (Fillion) is a famous mystery novelist who has killed off the main character in his popular book series and has writer's block.

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.

Club reviewer called the show "This is a cute piece of work that coasts largely on the charms of its cast".

[28] Michael Crider from Screenrant was also negative towards the show's premise as he said "Without the light-hearted and even flirty back-and-forth, there’s not a whole lot to distinguish Castle from any mystery made in the last twenty years".