The friars of a poor war-ravaged monastery find an infant abandoned on their doorstep. Having nowhere to turn in the wake of the Mexican revolution, they decide to raise him in the monastery, they name him Marcelino. The child grows into a rambunctious boy, fond of playing jokes on the friars but yearns for a mother as he observes the deep bond his best friend Eleuterio shares with his mother. Marcelino's curiosity leads him to the attic of the monastery, the one place he was warned never to go.