Five centuries ago, Pope Leo X issued a mysterious bull, according to which the Eternal City should “never, never, never” be plunged into darkness. But today, a storm has knocked out one of Rome's power plants, and in order for power to be fully restored, the capital will have to plunge into darkness for twenty-four hours. In the approaching twilight, hidden evil comes to life. No one is safe, not even those who double-lock their doors. A chain of murders stretches across the city, but who is the mysterious executioner, who is pressing the hidden springs. Marcus and Sandra must discover the source of evil before it's too late...