Don Giovanni loses his home and his possessions after a massive wave destroys the city he grew up in. He wanders about for a bit before a run-in with a demon or devil, in which the dark creature offers him a wager: an endless purse, all the money he could desire, but in return, he must not bath, change clothes, or clean himself in any way, for three years, three months, and three days. At the end of his rope, Giovanni accepts, hardly understanding what he is getting himself in for.
With thought-provoking philosophy on loyalty, persistence, and the value of wealth, and a nice dose of history, I'd call this one of Napoli's most successful retellings. Well worth reading, especially if you've enjoyed her other work.