A giant asteroid is headed toward Earth. Dexter goes into space in his giant robot, Robo-Dexo 2000, and uses a beam to try and stop it, but he breaks it into a group of asteroids, which hit his robot. Dexter has to call someone to help him stop the asteroids from hitting the Earth, and the only person available for this is Mandark. Mandark wants to do this himself, so he goes in his giant robot, the Mandark-Bot, to stop the asteroids, but he is also unable to do it alone. Dexter and Mandark decide to team up to destroy the asteroids, and they build another robot that they can both use to do this. But when they go into space they start fighting and get distracted, so the asteroids hit and destroy the Earth. Dexter and Mandark continue to fight over whose fault it was.
This is the second time when Dexter and Mandark are fighting.
Out of all the episodes in the entire series, this one is arguably the least canonical due to the episode ending with Earth destroyed and most of the characters outside of Dexter & Mandark ending up dead.
When Dexter and Mandark are about to hit their ejector buttons, their voices matched up with the wrong halves of the ship.