Young and naive 19-year-old slacker, Adam (Jack O'Connell (actor)), lives with his mum, Nicky (Kierston Wareing), in the home of her intimidating gangster boyfriend, Peter (Peter Mullan) and is sent to conduct a day of driving for Peter's associate after Adam inadvertently views an incriminating video on Peter's laptop. This takes Adam on the road with aging hitman, Roy (Tim Roth), as he enters a world of murder for 24 hours. Roy tries to force him to kill a mysterious girl (Talulah Riley) in a forest, but he refrains from doing so, giving her the chance to escape and drive away in their vehicle.