Earthman Roy Crawford is framed for murder on the planet Velliran. He has two choices. He must escape from the planet within three days or go to prison for life. But the only spaceship leaving the planet within three days belongs to the Exploration Corps. This is a group of scientists which investigates new planets. They are about to leave for World Seven on the Star System Z-16. With help from his friends, the dazed Crawford finds himself in the ship. The scientists, of course, think he is one of them. But World Seven is no escape for Roy. It is a planet of death. The team of scientists find themselves in a world where even the trees are killers. And one more killer is on the spaceship - the real murderer who framed Crawford!