A fight for survival in an alien world. Revenge is planned against Unity. Denver, Charlie and Layla are trapped in the middle of a galactic conflict which has spanned across many millennia. With no immediate allies on either side, they must use all of their skill and strength to stay alive and find a way back to Earth-if there is one. An old enemy of Unity is intent of making them pay for his humiliating treatment. He's gathering forces to the south with vengeance in mind. Mike and Mae must work together with the citizens of Unity to find a way of repelling Augustus' force, or face extinction at the hands of the old emperor. Critical Strike is the republished exciting third instalment of the Invasion Trilogy.