Guardians of the High Frontier: The Lunar Threshold
The Moon was never silent. It was waiting to be understood.
After the events of The First Starship, Vanguard enters lunar orbit under Dr. Thomas Faust's command, tasked with investigating impossible evidence buried near the Moon's south pole. What first appears to be an ancient industrial mine soon proves to be something far more unsettling: a vast, active system routing heat, charge, and Helium-3 toward a deeper structure hidden beneath the regolith.
As Naomi Caldwell and the science team struggle to interpret what they have found, political pressure from Earth closes in. Rival powers maneuver in cislunar space. Ship systems begin to fail under lunar dust, radiation, and forces the crew does not fully understand. Every answer carries a cost, and every cautious step may teach the buried system something new.
When a mission to confirm the truth ends in tragedy, Vanguard must decide whether restraint is still possible, or whether observation itself has already become contact.
The Lunar Threshold is the second book in the Guardians of the High Frontier series, a hard science fiction story of first contact, political tension, and procedural dread. Humanity came to the Moon looking for evidence of an alien mine.
What they found was only the plumbing.
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