While the Starmen are searching Mars for the lost race of Benefactors, an organized crime boss is getting the authorities to chase them down - by falsely accusing them of his own murder. He is also working for the Xenobots, who are searching for their 'ancient enemy' and who will stop at nothing until they find and destroy them. Zip, Mark, and Joe flee crooked cops, Xenobot robotic fighters, and Xenobots themselves in the Martian outback. Joe is captured by the mob boss, but Zip and Mark escape to hide in Martian caves. But they are trapped there. How can they escape to continue their search for the Benefactors, who hold the key to defeating the Xenobots and saving humanity?