After attempting to investigate a nearby planet, the reconnaissance Eagle goes haywire and crashes on the moon. Two of the crew were injured; Commander Koenig lay in a coma. Meanwhile, Koenig has been brought to the planet Zenno (which was not the planet they were investigating) to be studied by Raan, an alien anthropologist who considers mankind to be their "missing link". Koenig is informed that his body on Alpha will soon perish and he will spend the remainder of his life on Zenno as a "guest" to be subjected to one psychological experiment after another.