The film opens following a man as his plane lands at a private hangar and he makes his way to his mansion with his armed guard escort. The man changes into his swimwear and proceeds to get into his private pool to have a swim. As he swims he notices his watch at the bottom of the pool and swims down to retrieve it. An unknown man grabs the swimming victim and holds him under until he dies. The assassin, Arthur Bishop (Jason Statham), then uses the chaos that follows to take a careful route out of the mansion and to a nearby river where he jumps in and makes his escape. Back home, Bishop meets with Harry McKenna (Donald Sutherland) whom Bishop regards as a friend and mentor figure. Harry pays Bishop for his work in Colombia and they discuss Harry's son Steve McKenna (Ben Foster) before parting ways.Returning to his house, Bishop checks for his new contract only to find that it is to kill Harry. Bishop phones his employer to verify that the contract is correct and upon confirmation he requests a face to face meeting. Bishop meets with Dean (Tony Goldwyn) who tells him about a failed mission in South Africa in which assassins of the agency Bishop works for were killed. Dean tells Bishop that only two people knew about the mission, Dean and Harry, and that Harry had received money in exchange for the contract details. Bishop reluctantly kills Harry and makes it look like a carjacking. At Harry's grave Bishop meets Harry's son, Steve. Steve tells Bishop that he's going to go out and find any carjacker and kill them as revenge. Bishop secretly follows Steve and interrupts him killing a carjacker that he had run into. Bishop recognizes the raw potential of Steve and decides to train him as a "Mechanic". He adopts a chihuahua and instructs Steve to take the dog with him to a coffee shop each day at the same time. As Steve settles in to his routine Bishop escalates his training by taking him on a contract to show him what it's like. After Bishop strangles the man with a belt and stages it to look like an auto-erotic asphyxiation accident, he shows Steve all the planning that went into that assassination.Bishop informs Steve that he has a contract of his own. The target is a mechanic for another agency named Burke (Jeff Chase), who frequents the same coffee shop Steve has been going to. Furthermore, Steve is told that Burke's only weaknesses are that he is interested in young men and small dogs (such as the chihuahua they adopted). Burke makes his move on Steve and invites him out to drinks. Bishop instructs Steve to slip a large dose of Rohypnol into Burke's drink to cause an overdose. Steve ignores this direction and instead goes with Burke to his apartment. As Burke begins to undress, Steve attempts to strangle him with a belt as he had seen Bishop do. They engage in a struggle, and Steve manages to kill Burke after much effort. Bishop is later contacted by Dean, who expresses his disapproval of Bishop's use of Steve for the Burke contract. Bishop replies that he was given that contract through Harry and not Dean. Angry at his indignation, Dean informs Bishop that he's on a short leash.