Rose (Emily Blunt) is a beautiful, quick-witted con artist, who is making a killing selling fake paintings. But when she pushes one scam too far, she finds the mob on her tail and a price on her head.

Enter Victor Maynard (Bill Nighy), Europe's most efficient and expensive assassin. Keen to uphold his family's legacy for lethal efficiency, Victor embarks on his latest assignment with his usual solitary professionalism. Yet every time Victor has Rose in his sights something seems to hold him back.

Increasingly entranced by the spirited Rose, Victor spares her life, accidently acquiring a young apprentice (Rupert Grint) in the process. Believing victor to be a private detective, his two new companions tag along, while he attempts to deal with his feelings for Rose and the murderous attentions another hitman sent to finish the job.