Nicola Bryant

A visit to the Grand Canyon begins with disaster for the Doctor and Peri, when the TARDIS plunges into a ravine. The travellers' only hope is to descend to the valley on foot and then track the course of the Colorado river. Their perilous journey is fraught with danger, even before they encounter a band of 19th Century explorers led by Major John Wesley Powell. Joining the watery expedition, the Doctor and Peri begin to despair of ever seeing the TARDIS again. As food supplies dwindle, so do the group's options. This is a journey which some of them will never return.

The TARDIS lands aboard the Sun God, a vast spaceship carrying executives from a powerful 35th Century energy company. Peri is menaced by deadly cat-like robots, whilst the Doctor discovers that Spalding Revere, the company's founder, has set the ship on course for the heart of a sun. Spalding's last wish is to take his acolytes with him to the afterlife, and unless the Doctor can intervene he and Peri will be going with them. Tensions and in-fighting grow among the staff. Peri meets Brian, whose half-man/half-insect body has a terrible significance to Spalding's plan. As the Sun God continues on its final mission, time is running out for them all...