The father and mother of Jordan and Beryl Tavistock, British Secret Service agents, were murdered in Paris under mysterious circumstances. The orphaned children were raised by their uncle Hugh, also a former intelligence officer. At a party at their uncle's house, the brother and sister learn from tipsy guests that twenty years ago the police and intelligence services came to the conclusion that the traitor Bernard Tavistock killed his wife and then committed suicide. Beryl and Jordan are sure that the case was fabricated, but how to prove it? Brother and sister go to Paris to get to the bottom of the truth and defend the good name of their parents...