As the new planetary defense organization begins to take shape, the world it was formed to protect faces new threats. From beyond our solar system arrive hostile forces intent on our eradication. From within, the desperate grasping hands of the elite move to destroy that which they cannot control. Once again Sarah Thompson finds herself at the heart of the crucible. To face these dangers Sarah is joined by new allies, and the first class of the new international volunteer defense force. Together they must answer the question of how far they will go In Defense of Earth.