When an axe-wielding, escaped psychiatric inmate drops dead in Castle's P.I. office, Castle and Beckett's investigation leads Castle to suspect the victim's death could be the work of the Antichrist.
Season 8 Episode 21 of Castle was watched by 6,740,000 viewers, resulting in a 1.10 rating in the 18-49 demographic.
Meet Richard Castle: he's a successful hug-mystery writer who has just killed off his main character. However, it seems one of his fans liked his books just a bit too much when a copycat murderer starts running around killing people as described in Castle's books.
After being questioned by the police Richard joins forces with Detective Kate Beckett to solve this case. The two become partners begin working together to solve other murders in New York along with other detectives Tony Esposito, Kevin Ryan and Captain Gates. They also work with medical examiner Lanie Parish. Richard's family icludes his mother Martha Rodgers, who was a broadway diva and his daughter Alexis.