Myth-Ing Persons by Robert Lynn Asprin (Myth Adventures #5)

Skeeve is in a real pickle this time. His partner Aahz has disappeared, and it looks like foul play. Finding Aahz ought to be a snap for a talented magician like Skeeve, especially with a sassy apprentice and a dumb-but-brawny bodyguard along for the ride. The trouble is, they're sleuthing in another dimension: a strange and chilly realm where day is night and humans are considered monsters. Add a murder rap, a couple of vampires, and the fact that magic doesn't work here, and you've got a trio in real hot water—that is, unless Skeeve finds a different trick up his sleeve! Paperback, 1986 Goodreads: 3.99