Invasion - J F Holmes - Bog

In space, when you lose the high ground, you lose the war. Eleven years before, General David Warren was the best and brightest, in charge of defending the Earth from an attacking fleet. Over matched in battle, the Earth forces were devastated, and the enemy moved into the high ground and proceeded with orbital bombardment. Civilization fell, and then two years later, the enemy landed and the occupation began. Now Warren lives with his sister and nephew, trying to farm the land while avoiding detection by the occupiers, the Invy. When two travelers show up at his doorstep, his carefully constructed life starts to unravel. Humanity may be down, but not out.