Jimmy the Baker is dead. That doesn’t stop Castle from trying the free cupcake samples in his shop. They were made before Jimmy was shot dead into vat of chocolate sauce. The victim’s assistant says his boss got nervous when a black muscle car drove by earlier. Jimmy kept a briefcase filled with $50k in cash in his office. Beckett believes the bakery could be a front for the mob. A ruthless Irish mafia man named Bobby S owns a muscle car like the one that was seen at the shop. A bar owner named Siobhan O’Doul (guest star Cara Buono) had been in contact with the victim. She has a past with Detective Kevin Ryan back when was known as Fenton O’Connell.
Siobhan gives Ryan a passionate, flying lip-lock right in front of his wife, Jenny. Then she slaps him hard upon finding out he’s a cop. Ryan explains that he worked undercover for 14 months with the Irish mob before joining homicide. He ran with Bobby S. He also had a serious relationship with Siobhan, who is ticked because he left seven years ago without a word. Special Agent Sam Walker lets the team know that Jimmy the Baker was his informant. Siobhan is also working for him. They were trying to get a book known as the bible. It’s a ledger that could bring down Bobby S and his entire operation.
Agent Walker wants to send Siobhan back in. Ryan knows that’s way too dangerous. He volunteers to return Staten Island as Fenton O’Connell. No one is happy about this. Ryan hasn’t done undercover work in seven years. He’s bound to be rusty. Ryan heads off on his mission as Jenny stares at him without saying a word. Tears are in her eyes. It’s a delicate time for the couple. They’ve been trying to start a family. They are awaiting word from a fertility specialist to see if that’s even possible. Ryan assures Esposito that he knows what he’s doing just before he leaves with no gun, no wire and no backup.
Ryan enters Kelly’s Tavern. The place is filled Irish mafia. Ryan announces the triumphant return of Fenton O’Connell. He’s met with a whack to the face from Maggie, the wife of Bobby S’s number two man, Liam. Ryan meets with Bobby S. He wants to get back in business with him. Bobby S wonders why he shouldn’t just put a bullet in his head. Ryan disarms Liam with lighting speed. He hands the gun to Bobby telling him to pull the trigger himself if he truly doubts his intentions. It’s an intense scene, but Bobby buys into Ryan’s act. He welcomes his old friend back into the mix as a man of honor. Liam and his wife are skeptical of the new guy.