The premise is that there are literally millions of parallel Earths in existence, and that occasionally odd individuals have either had the natural ability or the ability under great duress to slip from one world to another - in a Fortean manner. When an inventor assembles a simple gadget that can be made from parts to be found at Radio Shack, with a potato for a battery, and distributes the instructions on its construction widely, the world is suddenly graced with thousands, or millions of universe-walking people, or Steppers.
And thus begins the interminable, or shall I say "Long," tale of people's travels in the universes of the Long Earth. I managed to stick it out about halfway through before sheer disinterest in the fates of any of the characters caused me to give up at last.
