In Venice, Homer's wife uncovers a decades-old conspiracy. Four-month summer holidays, spring break, and regular sabbaticals mean that Harvard professors Mary and Homer Kelly never have trouble finding time to vacation. Unfortunately, Homer's sideline as an amateur sleuth means that they rarely get to relax during their time off. And so, when Homer begs Mary to let them visit Venice to attend a conference in the famed rare book library of Cardinal Bessarion, Mary agrees on condition that Homer avoid any dead bodies. When they arrive in Venice, it is Mary, not Homer, who stumbles upon a murder. An intent sightseer, she combs the city with her camera, snapping pictures of anything that catches her eye. But when one of her snapshots captures something it shouldn't, Mary is sucked into a decades-old mystery that stretches back to the darkest moments of World War II.