John O'Toole is a hitman for the Irish Mob from Boston. He and his brother, Simon, came to Hawaii to kill Jimmy Sheehan, who was in witness protection for witnessing a hit carried out by the Irish Mob. They find Sheehan's girlfriend Suzy Green to question her about her boyfriend's location, not knowing that he's already dead, but the Hawaii Five-0 Task Force show up and he is arrested while his brother is killed by Officer Kono Kalakaua.