David Wilson is called “Pudd’nhead” by the townspeople, who fail to understand his combination of wisdom and eccentricity. He redeems himself by simultaneously solving a murder mystery and a case of transposed identities.

Two children, a white boy and a mulatto, are born on the same day. Roxy, mother of the mulatto, is given charge of the children; in fear that her son will be sold, she exchanges the babies. The mulatto, though he grows up as a white boy, turns out to be a scoundrel. He sells his mother, murders and robs his uncle, then blames the murder on Luigi, one of a pair of twins. Pudd’nhead, a lawyer, undertakes Luigi’s defense and, on the basis of fingerprint evidence, exposes the real murderer.

The book implicitly condemns a society that allows slavery. It concludes with a series of witty aphorisms from Pudd’nhead’s calendar.