Overview: With nothing to do on a quiet night, Ben takes the Fantasticar out for a spin and observes a spaceship in the sky. The spaceship abducts Ben, and the rest of the team attempt to track the ship down. The spaceship travels to the dark side of the Moon, and the commander of the ship, Sandro of the Centaurians, introduces himself to Ben. He tells him that they have been at war for a long time with the Polarians, and to end the war, each side has chosen a champion to fight for them. The Centaurians have chosen Ben to fight for their planet's supremacy and force him into the contest by threatening the Earth. Meanwhile, the rest of the team have tracked Ben down and hitch a lift on a Moon rocket. Inside an air-tight dome on the Moon, the Polarians led by Pollus arrive with their warrior, Monstro, a giant humanoid lizard. Monstro and Ben then compete with each other in a series of events, while Reed, Sue and Herbie enter the dome. Sue turns invisible and swaps the keys of the respective alien spaceships around. Ben and Monstro then work together and shatter the dome, causing the air to leak out. Trying to escape, the Centaurians and Polarians are unable to open their ships. Reed tells them that unless they develop a trust for each other and hand the proper keys back over, they will all run out of air.
