Never Trust a Dead Man — Vivian Vande Velde

SELWYN ROWESON HAS HAD A BAD WEEK.
First Anora broke his heart and decided to marry Farold, then Farold beat him up in front of the entire village, and then, Farold was found dead, with a knife hilt-deep in his back. Which might not be so bad, except it's Selwyn's knife, and everyone believes he is the killer.

As punishment, Selwyn is sealed in a burial cave with Farold's moldering corpse. Selwyn thinks he's doomed -- but then a witch appears in the cave and brings the dead man back to life to help Selwyn prove his innocence. Selwyn thought he disliked Farold when he was alive, but that's nothing compared to having to work by his side as they search for the real killer.