The Enterprise encounters a powerful energy force that has apparently killed all human life in a solar system with over one billion inhabitants. They identify the culprit as a small space probe that had its origins on Earth. Called Nomad, it merged with another and, as a result, took on a new mission to destroy all biological beings as being imperfect. It believes Captain Kirk to be its creator and, as such, has spared the Enterprise and its crew, at least temporarily.