Summary this episode : When a body is discovered in an industrial cake mixer, the murder is traced to an Irish gang and a bar owner named Siobhan O'Doul (Cara Buono); Detective Ryan reveals a history with Siobhan from his time working under cover in narcotics.

When mystery-thriller writer Richard Castle (Nathan Fillion) is called in to help investigate a series of copycat murders based on his books, he finds he enjoys the experience sufficiently to want to continue it. Pulling strings, he arranges to accompany NYPD Detective Kate Beckett (Stana Katic), claiming he wants to study and use her as a personality basis for his next book series. Once that initial case was solved, Castle and Beckett continued to investigate strange homicides in New York, combining Castle's writer intuition and Beckett's creative detective work. Over the past four seasons, Castle and Beckett's relationship has grown even stronger as they've dodged bullets, captured killers, and solved countless murder cases with their unorthodox partnership.