Elsewhere by Dean Koontz
Jeffy Coltrane receives "the key to everything" from a vagrant who seems to have a problem with reality. But then cold men in uniforms show up looking for the key, which helps its bearer jump through the multiverse to different worlds. Anyone who uses the key or knows of it is constantly hunted - but now Jeffy and his daughter have a chance to fill a hole in their lives. Is it worth the danger?
Wow, so Koontz really, really excels at pacing. This was unputdownable, even though it wasn't an excellent book. I did enjoy the fact that it was slightly different from other multiverse stories (less time in other worlds = fewer bogged down scenes), but I also felt that things were slightly too easy for Jeffy and co. And the bad guy was seriously stereotypical (you know the type, always the most deviant of deviants). A cracking read, nonetheless.
Alyce Caswell, when she isn't buried in a book or drinking her way through a giant pot of tea, is a keen writer of science fiction and romance. She has published two novels and four novellas in her space opera family saga, The Galactic Pantheon Series.