Leaving Concord, Massachusetts, for a six-week sabbatical in Venice, Professor Homer Kelly finds bliss at a rare-books conference while his wife, Mary, sets out to photograph the magnificent churches, palaces, squares, and waterways of the city. Elsewhere, golden treasures, hidden for half a century, lead to a vicious killing. During one of her tourist excursions, Mary snaps a picture of the extremely handsome murderer who befriends and then seduces her. Soon, holy artifacts begin to disappear as the acqua alta rises with the body count. When the streets are flooded and the moon is full, temptation overwhelms, bullets fly, and Homer and Mary learn that even their closest friends are hiding secrets that could end in death. In a city of legendary wonders, the Kellys will need nothing less than a miracle to survive.