Su único hijo tells the story of a monotonous and boring life in a provincial town that changes following the arrival of an opera company. Bonifacio Reyes, a husband and dreamer, becomes involved with one of the singers. Meanwhile, his wife Emma becomes involved with a baritone. Then, disillusioned with his lover and deceived by her political family, he has a profound moral revelation at the end of the novel, ennobled after rejecting the justified suggestion that he is not the father of his wife's son. The central theme of the story is parenting as a means of redemption.