A man named Bob Carson wakes up naked in a dome. He is lying on blue sand and there are several blue-colored plants around him too. However, he seems to be alone. At first, he does not remember why or how he got there.

Carson starts to gain his memory back, remembering that he was orbiting Pluto scouting the area for Outsiders so the Earth Armada could attack. Those on Earth don't know who the Outsiders are, but they have raided Earth many times. Also, their ships aren't as fast as those on Earth. He had been scouting and found an Outsider ship. Swerving to avoid the ship, Carson crashed into a planet and blacked out. He now finds himself in this blue dome.

While he sweats from the heat, he hears a voice. It tells him that it is of an old race that seeks to intervene between the fight of the humans and Outsiders. However, in order to determine what side it will choose, it forces Carson and a spherical alien (which Carson nicknames The Roller) to fight to the death. Whoever wins gets to continue their life and the other race will get wiped out.

When the voice leaves, Carson takes in his surroundings and his spherical opponent. The Roller keeps rolling towards him and stopping in the same place, which Carson realizes is due to a force field separating them. Carson attempts to ask The Roller for peace, but the creature communicates by sending nauseating anger in Carson's brain. While trying to create weapons, Carson realizes that the only things that can bypass the barrier are inanimate objects. He begins throwing sticks and rocks as projectiles. The Roller learns of this too and throws things back, injuring Carson's leg.

In pain and suddenly dehydrated, Carson takes a break from the fight to clean his wound and search for water, to no avail. Carson notices The Roller creating a catapult, but Carson is able to burn the first catapult down with fire he created by two rocks.

The next weapon Carson makes is a harpoon. He falls asleep and awakes to a dying lizard pleading to have its pain ended. The lizard came from The Roller's side, but Carson realizes that it is not inanimate objects that can't pass through. Rather, things that are unconscious can pass through. Carson takes his harpoon, digs a hole, and knocks himself out in order to pass through the barrier. As The Roller approaches, Carson is able to stab his harpoon into it.

After The Roller dies, Carson finds himself in his original scouting vehicle. The Earth Armada has destroyed the Outsider ship. According to his captain, something fantastical seemed to destroy their enemies. Carson knows this to be the being that set him up into the death match initially.