In 1982, Toronto bank employee Dan Mahowny (Philip Seymour Hoffman) is given access to bigger and bigger accounts with his promotion to assistant branch manager. His boss trusts him, but is unaware that Mahowny is a compulsive gambler. Mahowny is soon embezzlement larger and larger amounts for his own use and making weekly trips to Atlantic City, where he is treated like a king by a competent casino manager (John Hurt). Mahowny's girlfriend, fellow bank employee Belinda (Minnie Driver), cannot understand what is happening. Mahowny's criminal acts come to light when Toronto police begin to investigate his longtime bookie Frank (Maury Chaykin).