On Ceres, Starr plans to send his friend Bigman to infiltrate the pirates, but realizes that Hansen's asteroid is not where it should be.

Starr wakes to find himself in a spacesuit on the surface of the asteroid; whereupon Dingo straps him to a catapult and flings him into space.

Returning to Ceres, Starr realizes that the pirates' real object was to capture Hansen, which they have accomplished, and learns that Captain Anton's ship is taking Hansen to a secret Sirian base on Ganymede, whence the Sirians plan to attack Earth while Earth's fleet is occupied fighting the pirates in the Asteroid Belt.

Writing in The New York Times, Sidney Lohman praised Pirates as "grand science fiction for all ages.

[2] Astounding reviewer P. Schuyler Miller described it as "fast-moving space opera of a type we all know, with no particular regard for scientific plausibility.

"[3] Lucky Starr and the Pirates of the Asteroids introduces the Sirians as the main threat to Earth, and marks Starr's transformation from his masked crime-fighter role of the first novel to a Cold War-like secret agent.The novel contains the first hints of an overpopulated Earth facing the hostility of the younger worlds of the Galaxy.