On a desolate, storm-lashed planet called Morganthus, the last survivor of a crashed spaceship is attacked and killed by an undead crew member. On Xerxes, another planet a very long distance away, two figures are seen playing a strange game. One, an old woman named Mitri, is identified as the controller of the game while the other, whose head is obscured by a glowing ball of red light, turns out to be an all-powerful mystic called the Planet Master. The two speak cryptically of things being put into motion, and the Master instructs Ilvar, one of his military commanders, to send a ship to Morganthus.
Without delay, the spaceship Quest blasts off to Morganthus, piloted by Captain Trantor, a survivor of a famous space disaster that has left her psychologically scarred and unstable. As the Quest approaches the planet’s atmosphere, it suddenly veers out of control; slowly the captain realizes she can control the ship as to its approach to the planet, but still plunges toward the surface and makes a survivable landing. After recovering from the crash, the crew prepare to leave the Quest and search for survivors. Among the crew is a psi-sensitive woman named Alluma. She and other team members have significant problems with pushy and arrogant team leader Baelon, who is unimpressed by Alluma’s inability to detect any lifesigns whatsoever.
Crossing the landscape of the planet, they eventually reach the other vessel where they find evidence that a massacre has taken place. The rescue teams split into two and explore the craft. The discovery of more victims all but confirms the occurrence of a massacre. The team disposes of all of the bodies except one which they take back for analysis. Cos, the highly-strung youngest member of the team, becomes increasingly terrified of being on the ship despite being reassured by his seniors. This is the first clue that it is the fear of the individual crew members that are manifesting to kill them. A short time later, he is killed by a grotesque creature.
The crew discover that something from the planet pulled them down and, in order to escape, they must investigate. While Trantor, Kore, and Ranger remain on the ship, Cabren, Dameia, Quuhod, Baelon, Ilvar, and Alluma explore the planet. They discover a massive pyramid-shaped structure, which Alluma describes as “empty” and “dead”. They find an opening at the top of the pyramid and use a rope to slide Ilvar in; Ilvar is attacked by tentacles that drain his blood. They find an alternate entrance, though Quuhod breaks his crystal throwing stars and remains by the entrance. The throwing stars reform; when Quuhod picks one up, a piece breaks off and begins sliding through his skin, forcing him to sever his arm. However, his arm uses the remaining throwing star to impale him.
The crew continue to search through the pyramid. When Alluma voices a desire to leave, Baelon refuses to allow it. An angered Dameia wanders into another area and discovers Quuhod’s severed arm being eaten by maggots. One maggot grows to giant size and proceeds to sexually assault and kill Dameia. Back on the ship, Ranger catches sight of Trantor on the security cameras as she spontaneously combusts. He races to save her, but by the time he reaches her, her skin has completely burned off. After discovering Dameia’s corpse, they head back to the ship.
The remaining crew return to the pyramid. There, Baelon elects to stay behind and is torn apart by a monster. Meanwhile, inside the pyramid, Alluma, Ranger, and Cabren are separated by moving walls. Alluma is attacked by tentacles which crush her head, while Ranger is attacked by his double. He manages to fend the double off, and it disappears. Deep inside the pyramid, Cabren discovers that Kore is really the Master, who has been masquerading as Kore on board the Quest. He tells Cabren that he has “won the game.” The Master then explains that the pyramid is actually an ancient toy for the children of a long-extinct race, built in order to test their ability to control fear. Cabren is then forced to confront the creatures which attacked the crew as well as zombified versions of the dead crew, all of which he kills. Finally, Cabren kills the Master’s previous host body, but as the master cannot be killed, Cabren takes his place. Cabren states that he will not play this game, and will simply leave the planet. Kore’s dying words express doubt that Cabren will be able to change his fate.