Don't let the age of this book put you off as it was well ahead of it's time. It's fast, with dry humor on how you live in the modern world with magic, werewolves (what if you had a job as an actor playing a wolf??) and witches. There is also plenty of suspense, lots of action, romance and though not an outstanding read - it's very entertaining, memorable and a worthwhile armchair adventure.
It was Earth, but not Earth as we know it. Overhead, the stars were like cinders in a flat and bone-gray sky. A man and a woman stood on a plain with no horizons, shivering in the thin, cold wind. They had just opened the Door between the worlds, and something was coming to greet them . . .
Great imagination from the author of the Ensign Flandry & the Space Merchants