At night in her bayside mansion, wheelchair-bound Countess Federica (Isa Miranda) is attacked and strangled to death by her husband Filippo Donati (Giovanni Nuvoletti). Moments later, Filippo himself is attacked and brutally stabbed to death by an assailant, and his corpse is then dragged to the bay. Upon investigation, the police find what they believe to be a suicide note written by the Countess, but Donati's murder goes undiscovered.