When a huge cloud approaches the Sol system and threatens to destroy all life on Earth, Admiral Kirk assumes command of the newly refitted Enterprise, reducing Capt. Decker to his first officer. On their way to intercept the cloud, Spock, who sensed its presence when he was on Vulcan, rejoins the crew. When the entity that calls itself "V'ger" scans the ship, the Deltan navigator Lt. Ilia is absorbed and later returned as an android. Spock and Kirk find out that V'ger routinely scans and saves everything it encounters along its path. V'ger turns out to be an enormous machine built for the sole purpose of seeking for and eventually merging with the Creator of its distant relative, the space probe Voyager 6 that was launched from Earth a long time ago. The entity is accordingly unsatisfied when it discovers that humans, primitive "carbon units", were the Creators. But V'ger, in the form of the Ilia probe, agrees to merge with the Creator, in the form of Capt. Decker, to a totally new lifeform.