Communion, by Saucery
An incubus and a priest team up with a witch in order to save the world. Or, a supernatural version of The Man From U.N.C.L.E., complete with evil demons and hotel sex.
Adult, AU, possible dubcon. Incubus Napoleon wants priest Illya to sate his hunger, Illya just wants him to leave Gaby alone. They both get more than they expected.
ETA: Fic seems sadly to have been deleted, but there’s a podfic available.