Life on the desert planet Penumbra is cruel and unforgiving, but Jonathan Crowe is more than familiar with it. He and his teenage son, William, brave the desolate terrain day and night with their jobs as rover wranglers. For them, a brush with danger is all in a day work from the scorching heat to the screamers that prowl the sands. They risk it all for the greater good of the colony they live in. However, nothing strikes fear more than Penumbra's native inhabitants, the Aksems. A race of human-like warriors, the Aksems are known for their natural aggression and brutality. They devastate the lives of everyone they come across and then vanish, leaving carnage in their wake. Jonathan has seen what they are capable of firsthand, but discovers there is more to them than he thought. The father and son receive hands on experience full of surprises and an insidious part of their primal culture.