What Mark Twain novel features a fingerprint-based plot?

Mark Twain's novel featuring a fingerprint-based plot is Pudd'nhead Wilson.

Published in 1894, Pudd'nhead Wilson centers on a mystery in which fingerprints help expose the truth behind two boys switched as infants. The boys grow up in radically different social positions, one treated as white and privileged and the other connected to slavery and racial oppression. Their physical resemblance makes the switch difficult to detect for years.

The title character, David Wilson, is a young lawyer whose clever remark earns him the insulting nickname “Pudd'nhead.” He also has an unusual hobby: collecting fingerprints. The townspeople dismiss this interest as eccentric, but the technique later becomes crucial to identifying the characters and untangling the deception.

The novel was serialized in The Century Magazine from 1893 to 1894 before appearing in book form on November 28, 1894. Its fingerprint plot is tied to Twain's satire of racial classification, slavery, inheritance, and the danger of judging identity by social labels or appearance. It is therefore both a mystery and a pointed social critique.