The coffee maker in Barracks 3 dies at 0447. Turret 4 is offline again. Staff Sergeant Thorne has six years on Veridian IV, a flickering eye implant, and a morning inspection that will not wait for replacement parts. Then the perimeter actually goes. Contact front, a chain of command that breaks, reinforcements denied, water wars, a reactor secret, a double cross, and a last-stand protocol that includes negotiating with monsters. Perimeter Breach is garrison military SF: field-expedient solutions, salvage, a tunnel run, and an after-action report written by people who were not supposed to still be there.