Every time Zaxony Delatree falls asleep he wakes up on a new world. His life has turned into an endless series of brief encounters. But at least he and Minna, the one companion who has found a way of travelling with him, are no longer pursued by the psychotic and vengeful Lector.

But now Zax has been joined once again by Ana, a companion he thought left behind long ago. Ana is one of the Sleepers, a group of fellow travellers between worlds. Ana tells Zax that he is unknowingly host to a parasitic alien that exists partly in his blood and partly between dimensions. The chemical that the alien secretes is what allows Zax to travel. Every time he does, however, the parasite grows, damaging the fabric of the Universes. Anas is desperate to recruit Zax to her cause and stop the alien.

But there are others who are using the parasite, such as the cult who serve the Prisoner - an entity trapped in the dimension between universes. Every world is like a bar in its prison. The cult want to collapse all the bars of the worlds and free their god. Can Zax, Minna, Ana and the other Sleepers band together and stop them?