The fourth book of the military science fiction series The First Line
The alien ship attacking Earth may have been destroyed, but with Mars still under the control of the Longshanks, the remnants of Earth's armed forces are fully focused on replenishing the fleet and defending the planet instead of celebrating. Platoon Sergeant Andrew Grayson contributes to the overall effort as an instructor who extensively prepares new soldiers for duty. But for the battle-scarred sergeant, it's getting to be a boring routine.
The North American community and their new Sino-Russian allies are all too aware that Earth has received only a brief reprieve, and see only two options for moving forward. Either they will immediately attack the Longships on Mars, or they will go after the deserters and their fleet of modern ships that could tip the balance of power in the coming battle for Mars. A small special operations reconnaissance unit follows the trail of the deserters, and Grayson once again finds himself in the middle of a battle on a distant moon that will determine the future of humanity.
