Rome, 1923. Rex and Dora's holiday comes to an abrupt end when they receive an urgent message from Rome. The Carabinieri have accused the British ambassador of murder. A witness puts the ambassador at the scene, and the evidence points to his guilt. But he assures the couple he is innocent. If the Carabinieri are allowed to proceed with their accusations, this simple case will become an international incident. Rex and Dora face their most difficult puzzle yet. First, they have to uncover the real identity of the victim. Only then can they determine who had the motive to kill. But in the Eternal City, the past and present are intertwined. Old flames return, past grudges re-emerge, and regrets bring consequences. Before the case ends, they'll have to answer a riddle. What is more important—solving the case or saving the life of a friend?