London, 1958, Ena recognises a woman who she exposed as a spy in WW2. Ena’s husband, Henry, an agent with MI5, argues that it cannot be the woman because they went to her funeral twelve years before.

Ena, now head of the Home Office cold case department, starts an investigation. There are no files. It is as if the woman never existed. Suddenly colleagues who are helping Ena with the case mysteriously die… and Ena herself is almost killed in a hit-and-run.

The case breaks when Ena finds important documents from 1936 Berlin that prove not only did the spy exist, but someone above suspicion who worked with her then, still works with her now. Fearing for her life, there is only one person Ena can trust… or can she?