Duffy and the Devil was a popular play in Cornwall in the nineteenth century, performed at the Christmas season by groups of young people who went from house to house. The Zemachs have interpreted the folk tale which the play dramatized, recognizable as a version of the widespread Rumpelstiltskin story. Its main themes are familiar, but the character and details of this picture book are entirely Cornish, as robust and distinctive as the higgledy-piggledy, cliff-hanging villages that dot England's southwesterncoast from Penzance to Land's End.

The language spoken by the Christmas players was a rich mixture of local English dialect and Old Cornish (similar to Welsh and Gaelic), and something of this flavor is preserved in Harve Zemach's retelling. Margot Zemach's pen-and-wash illustrations combine a refined sense of comedy with telling observation of character, felicitous drawing with decorative richness, to a degree that surpasses her own past accomplishments.

Duffy and the Devil is a 1973 New York Times Book Review Notable Children's Book of the Year and Outstanding Book of the Year, a 1974 National Book Award Finalist for Children's Books, and the winner of the 1974 Caldecott Medal.