Summer, Matthew and Tara are three friends accidentally transported aboard a vast spaceship when aliens raid Earth, stealing treasures and priceless artefacts. The aliens are running from a Fundamental, an original inhabitant of the original universe.

Although they are -mainly- welcoming, the aliens refuse to take the children back to Earth. The Fundamental is trying to find them, enslaving planets and stripping them of their resources along the way.

The children decide they have to try and find their own way home, despite being hundreds of light years from Earth. Their plans meet with little success and put the fleet in danger before they discover a shocking secret that changes everything.

At the same time they realise that there is a spy and saboteur on one of the ship. Torn between finding a way home and helping the aliens, the children face a series of hard choices with consequences for the inhabitants not just of the fleet but for Earth itself., whose sole aim is the destruction of the fleet.