Tom Hanks plays Michael Sullivan, a gangster regularly sent to kill people in the course of his work for John Rooney (Paul Newman). He also has a wife and two sons, and comes home to a conventional home life. His wife knows about his work, which they have kept from their sons. This state of innocence lasts until his eldest, Michael Jr (Tyler Hoechlin), hides himself in his father's car and witnesses his father involved in a violent murder with Rooney's adult son Connor (Daniel Craig).
Connor, fearing that the boy will tell what he has seen, sets out to kill him but mistakenly kills the younger brother instead, along with their mother. Rooney, who did not approve this killing, is angry but sends Connor away for his own protection. Sullivan and Michael Jr take to the road, seeking both safety and Connor, closely pursued by contract killer Harlen Maguire (Jude Law). Now beyond the protection of his gangster family, it is his son that Sullivan must turn to for support as they set out for the home of 'Aunt Sarah' in Perdition a place which both have imbued with idyllic qualities in their own minds.
This isn't just a gangster film, but a father and son story. Sullivan is at once a notorious killer, even amongst other killers, and is at the same time a loving family man with a code of honour that he will not break. This is the story of the six weeks on the road in which Michael Jr comes to truly understand his father.