“The Adoration of the Mystic Lamb” is a work that has been so adored that it has become infamous as the most stolen artwork in history. Of all the many times the piece was stolen, however, there is one incident that stands above the rest as probably the most significant theft, because it is the only time that part of the painting went missing, never to be seen again. It is an enduring historical whodunit that deserves to be remembered.