**This “marvelous lunar espionage thriller” by the science fiction grandmaster and author of *2001: A Space Odyssey* “packs plenty of punch” (SFReviews.net).** Two hundred years after landing on the Moon, mankind has moved further out into the solar system. With permanent settlements now established on the Moon, Venus, and Mars, the inhabitants of these colonies have formed a political alliance called the Federation. On the Moon, a government agent from Earth is tracking a suspected spy at a prominent observatory. His mission is complicated by the rise in tensions between Earth’s government and the Federation over access to rare heavy metals. As the agent finds himself locked in a battle for life and death on the eerie, lunar landscape, the larger conflict explodes across space, leaving mankind’s future in doubt. First published in 1955, this suspense-filled space opera by the Science Fiction and Fantasy Hall of Fame inductee was a significant forerunner of television hits like *Star Trek* and *The Expanse*.