The broadcast interview of a young computer prodigy attracts the attention of aliens aboard an interstellar trading ship. The kidnapping of Tommy (and his cat) begins an adventure among the stars, a coming of age story entangled with computers, faster-than-light travel, a dying civilization, and an ancient evil. Once on board a five-thousand-meter starship, Tommy meets a crew of humans, descended from peasants, priests, and soldiers taken from Earth a thousand years before, all slaves to seldom-seen aliens inhabiting the upper third of the ship Tommy is expected to replace the ancient and failing computers on the ship with computers taken from Earth, beginning with the long-dead missile controller, without which the ship is defenseless. After the new missile controller, with Tommy as its operator, successfully defends the ship against attack, his "benefactor," one of the alien Nesu masters, directs him to replace the environmental and navigation computers. This work leads to the discovery that the star drive is from still another alien group who, fifteen hundred years before, destroyed the Nesu home world and now limit all scientific advancement in the local arm of the galaxy, including Earth.