Riley Cavanaugh is an enforcer for the Irish mob who worked for his boss, George Massey. According to Detective Bill Szymanski, Riley is believed to have committed three mob related hits under George's orders from 2010-2012. He was ordered by George to kill Sean Delaney because he was stealing from him and was then sent to keep an eye on his widow Annie but he fell in love with her. When Annie continued to press George about her husband's murder, George ordered Riley and his son Eddie to kill Annie. However, George had learned of Riley's relationship with Annie and ordered Eddie to kill them both. Realizing this, Riley kills Eddie in self-defense, resulting in George putting out a million dollar bounty on both Annie and Riley.
With the help of Elias, Reese and Finch were able to get the bounty called off, but Ochoa went after the two anyway, kidnapping Annie as Riley got her a train ticket to New Mexico. Riley teamed up with Reese and infiltrated George's nightclub with him. With Reese as backup, Riley engaged the mobsters in a shootout, killing them all with Reese's help and getting Annie to safety. As he fights the mobsters, one shoots Riley at the same time he kills the mobster. Wounded, Riley kills George before being murdered by Ochoa. Reese later found Riley's body and retrieved the ticket he bought Annie.
Reese uses the ticket Riley got Annie to send her to New Mexico to start a new life as he'd wanted. Annie realizes Riley was never coming with her which Reese confirms, telling her that Riley knew she'd never be safe with him around. Reese tells Annie that Riley had told him Annie was the best thing that ever happened to him and he and Finch realize that people do change, even killers, thanks to Riley. Later, Reese tracks down Ochoa and presumably kills him to avenge Riley.
- Three mob related hits carried out on George Massey's orders from 2010-2012 (presumed).
- Sean Delaney - Shot on George Massey's orders.
- Eddie Massey - Shot twice in the side with hollow-point bullets in self-defense.
- Two Irish mobsters - Shot in self-defense.
- John Reese - Shot, protected by a bullet-proof vest. Attacked later but defeated.
- Five Irish mobsters - Shot rescuing Annie Delaney.
- George Massey - Shot rescuing Annie Delaney.
- Finch tells Reese that Riley is Bad Code, although he changes his opinion after Riley's death