"You are now a discard. We have no further use for you in play. You are free to walk the Bounds, but it will be against the rules for you to enter play in any world. If you succeed in returning Home, then you may enter play again in the normal manner."
When Jamie unwittingly discovers the sinister, dark-cloaked Them playing games with humans' lives, he is cast out to the boundaries of the worlds. Clinging to Their promise that if he can get Home he is free, he becomes an unwilling Random Factor in Their deadly, eternal game.
Jamie travels alone until he teams up with Helen and Joris, determined to beat Them at Their own game. But Their rules don't allow Homeward Bounders to work together.