While exploring the countryside on holiday, Tom and Geoff fall into a cave, where they find the skeleton of a Roman Centurion. Alongside the skeleton is a strange pod, with the name Aquila written on its side. After climbing into the pod, Geoff rashly presses one of the flashing buttons and Aquila instantly moves upwards, stopping in mid air fifty feet above the ground, with the boys still inside it. They quickly discover that Aquila is a remarkable flying machine, and realizing that it will be taken away from them as soon as they tell anyone, they decide to keep it a secret.
—Phil G