The Portable Door - Tom Holt

Starting a new job is always stressful (especially when you don't want one), but when Paul Carpenter arrives at the office of J. W. Wells he has no idea what trouble lies in store. He is about to discover that the apparently respectable establishment now paying his salary is a front for a deeply sinister organisation that has a mighty peculiar agenda. It seems that half the time his bosses are away with the fairies. But they're not, of course.They're away with the goblins.