 When a policeman is murdered for interrupting an organized-crime transaction, McGarrett hauls in the killer -- only to see him walk when an FBI agent investigating a much larger organized-crime ring offers the killer immunity from prosecution if he ll testify. McGarrett protests strenuously, but he and the Fed are forced to team up when the syndicate sends a hit man after the informant -- and anyone else who gets in his way, including McGarrett and the Federal officer.