Ben (14) lives in the "nothing-ever-happens-here" town of Werrinup on the coast. One day he discovers a portal into a parallel universe and that there he has an older sister, Katherine. It gets even more interesting when he meets a boy who is the parallel world doppelganger of his best friend Francis. To Ben this is all pretty cool, and a welcome change of pace to life in a small country town. Ben and Katherine find friends and allies in other parallel universes. Mundi, for example, comes from a world where the natural environment is respected and her community live in houses built high in the trees. Technology and consumerism is triumphant in another Werrinup where the town and its river are part of a modern high-tech suburb of a major city. It is mainly fun as the kids explore the worlds of the Parallax - until they find a world that is a desolate ruin. It is then that they realise that there is a threat in the Parallax that is both dangerous and very close. They discover that the information they need to save their worlds may be held in the Reading Room, the Guardians' repository of all the knowledge from all the worlds in the Parallax. The problem is that the Guardians can no longer gain access to the Reading Room. When their mother Veronica disappears, Ben and Katherine embark on a quest to find both her and the missing key to the Reading Room. It is a quest that leads them to the mother of all hostile welkin (large snake-headed wasps), an army of purple crab-clawed krellicks, a rather dangerous Aunt Betti, many chickens and - after all - the Lost Guardian?