A besieged Earth has fallen to the alien Invid horde. The planet's scattered and war-wearing defenders must band together and fight as never before if their home is ever to be free again, but the enemy is not always alien. Many people are so tired of war they will take peace at any price, even if it means betraying their fellow men and women to the Invid occupiers. What hope do Earth's freedom fighters have when they cannot tell friend from foe, and what unlikely allies will they turn to in their hour of need?