This document is an excerpt from "Doctor Who: Frontios," a novelization by Christopher H. Bidmead, based on a BBC television serial. The narrative centers on the Doctor, Tegan, and Turlough, who are marooned on the planet Frontios after their time machine, the TARDIS, crash-lands during a meteorite storm. Frontios is a refuge for the last surviving humans from Earth, who are under constant attack from mysterious "bombardments" and contend with strange disappearances into the planet's surface. The Doctor and his companions uncover the true nature of these threats, revealing a subterranean race called the Tractators who are responsible for the attacks and are harnessing the planet's gravitational energy for their own cosmic goals, while also utilizing the colonists' bodies for their machinery. The story details their efforts to understand and combat the Tractators, ultimately leading to a plan to disable their leader, the Gravis, and restore order to Frontios.