A year after her husband's death, young widow and art collector Diana Porteous listlessly roams the beach near her home. Her friend and agent Saul takes action, introducing her to his stylish, anarchic sister, Sarah, to pep her up. They plan that Di should rediscover her talents as a thief, as well as art expert, to recover stolen paintings - and begin with Steven, the neighbour's son, who is amassing works of art in a strange building in London, including work stolen from his mother.