Soon after Oliver the spaniel joins Beth & Kirsty's family, following his ill-treatment by his first owner, their family is confronted by property developer Mr Groose who will stop at nothing to buy their house in the picturesque village of Ayleswater for development. When he only has they and their friends the Periwinkles houses left to buy and things seem desperate the girls discover that they have small aliens at the bottom of their garden. These friendly creatures also want to stop the destruction of the house because it will destroy the vortex connecting their world to ours, which they use to observe humankind.
They enlist the help of Beth & Kirsty by giving them powers to embark on invisible astral explorations. After several dream flights of exploration to many corners of Britain and around the world they eventually discover Groose's horrible ideas for them. Somehow they must thwart those plans of his and his henchmen but unknown to them Oliver has a vital role to play in their final destiny. In their quest they also discover the real truth of an ancient legend in their village