On a brutal prison moon of Jupiter, a weary miner watches the inmates labor under Marnick, an Earthman overseer whose sadistic rule is enforced from a glassite cage and by rumors of savage punishments. His cold laughter drives the prisoners toward fear, rage, and the first sparks of rebellion, especially McGowan, a fierce Earthman whose hatred of Marnick has become a vow of revenge. When McGowan openly attacks the overseer, the act is futile but electrifying, and even defeat cannot silence the growing conspiracy beneath the tunnels. Reed is drawn into that conspiracy and led through hidden passages toward a daring escape plan built over years of secret digging. Because a laboratory accident has made him sensitive to directional beams, he must guide the men past Marnick's hidden alarms as they claw their way toward the surface. But escape proves only part of the design: McGowan also intends to strike at the man who ruined them, even if the price is betrayal. As the fugitives reach Marnick's lair, the trap tightens. Elson is sent to trigger the alarm and dies in the attack, and McGowan reveals the final cruelty of his revenge: Elson was Marnick's long-lost son. In the end, this grim science-fiction tale turns on oppression, sacrifice, and the terrible cost of vengeance. This edition has been fully restored with modern typesetting, custom cover design.