Demonprice, or, Doom of the Penultimate Husband — Phoebe Matthews

Demonprice, or, Doom of the Penultimate Husband, is the third Sunspinners novel. Elaine's second ex, Nathan, has sold 4/5ths of his soul to the devil and guess who he asks for help. Help! Charley and Elaine end up in the devil's vestibule with no way out.