It is 2,409 days after leaving Earth orbit, and is tracking an unidentified powered object following the Moon. Sensors detect no life forms and the craft is emitting an energy field highly sensitive to matter. The Alphans conclude the object to be a robot survey device. The object continues to close, the energy field making contact with the Moon surface. The instruments suddenly register a tremendous energy surge. As orders defensive measures, the object projects a ray at Alpha that not only penetrates the defence screens but underground into .