Ru-um and his younger brother Cali, on holiday in Northwest Scotland, go missing while on a walk to an ancient, ruined broch. Last seen with the mysterious girl, Amelia, they are eventually found several days later, unharmed, but with Cali now inexplicably older than Ru-um.

The story breathlessly follows the boys as Amelia takes them deep under the broch to the Flitspace - a gateway to another world identical to their own but completely uninhabited, except for the descendants of a small tribe who fled from Scotland one thousand years ago. However, Amelia hasn’t told them the whole truth of her world, or of the strange aging properties of the Flitspace. The boys quickly find themselves in conflict with Amelia’s powerful brother Mor-Ri and his enigmatic advisor known as Minister. With Amelia’s help, their own knowledge of the landscape, and the discovery of megafauna not seen in present day Scotland, the boys attempt to thwart Mor-Ri’s plans and escape back to their own world.