Detective Scotty Valens from Philadelphia's Cold Case unit comes to NY to investigate a murder that connects to Stella's past. Also Mac's recent solo bust is scrutinized because a handcuffed criminal fell of a rooftop.

An Irish gang sets an elaborate plot to reclaim a drug shipment being held at CSI after a bust, but Mac, Stella and Hawkes are forced to take them on. Meanwhile, Danny is being held as a hostage at another location by the same gang.