An American crime thriller film about an undercover state cop who has infiltrated an Irish gang and a mole in the police force working for the same mob race to track down and identify each other before being exposed to the enemy, after both sides realize their outfit has a rat.
When does he find out in the movie? Is it when he says on the phone: "So it is you. Thank God you're all right. We were very worried." And how exactly does he know it's Costigan? Sorry, I've watched ...