Rosie has been dumped for a younger woman by Piers, her middle-aged husband. Rosie is quietly living alone when Darren, the abandoned husband of Piers' pregnant mistress, tricks his way into meeting her. Darren's rage at being left ignites Rosie's and together they plot revenge. Darren also awakens long-latent feelings in Rosie and, as they embark on their unlikely romance, Piers' world starts to fall apart - with hilarious and surprising results.