A seventeenth-century Italian orphan finds the long-lost piece of The Last Supper, missing since Dominican friars cut out a portion of the wall to connect the priory's refectory with its kitchen. The painting has long ago dissolved, and the refectory converted to stables. The orphan boy sleeps in the stables, and he begins to have visions of the painting. Each night, the visions get clearer and clearer, until the boy sees the whole painting as Leonardo first painted it two hundred years before. But missing is the segment from the lower center of the painting, depicting the Christ's crossed feet, which was displaced by the kitchen door. With the help of the prior, two loyal brothers, and the twelve workhorses who share the stables with the boy (and whose presence he discovers is necessary to maintain his visions), the boy finds the missing piece of wall. But danger looms for all as soldiers of the Inquisition arrive to investigate the miracles.