Castle (2009)

S5E18 The Wild Rover

The discovery of a man's body in an industrial cake mixer leads Castle and Beckett to investigate an Irish gang operating in Staten Island, along with a striking bar owner named Siobhan O'Doul. In an unexpected twist, Detective Ryan reveals he has a tangled past with Siobhan and the crime family, stemming from his time as an undercover narcotics officer. As the investigation stalls, Ryan is pulled back into an undercover role to uncover the murderer, which strains his relationship with his wife.