A year has passed since the events in David Starr, Space Ranger. In that time the spaceship TSS Waltham Zachary has been taken and gutted by pirates based in the asteroid belt, and David "Lucky" Starr has come up with a plan to deal with them. The Council of Science has announced a project to thoroughly survey the asteroids, and the Atlas will be the first ship to conduct that survey. The Atlas, however, is a trap: it is unmanned, and as soon as the pirates capture it and bring it to their hidden asteroid base, it will explode. But Starr has a hidden motive for suggesting the Atlas project: twenty-five years earlier, space pirates attacked his father's ship, and both of Starr's parents were killed. Now, the pirates of the asteroids are back, and Starr intends to confront them in person. He sneaks aboard the Atlas just before it lifts off from the Moon.