Five, young astronauts found themselves stranded in orbit around Earth. Strange beings had taken the Earth hostage with a deadly green gas that could annihilate all life. After a pursuit and struggle, they managed to save the Earth, but at the expense of their pilot, Cathy, and a crew of Air Force soldiers. The alien beings escaped with them in tow as host bodies to carry out their insidious plans. Now, the N.S.S.A. has discovered a signal coming from the surface of the moon that could only be from the spacecraft that the entities, as they now came to call them, had hijacked. The Air Force immediately mobilizes soldiers from a new branch of specially trained Space Marines and launches what they say is a possible probing and/or rescue mission. Jennifer, Mark, Bruce and Kyle are brought onboard as advisors and because of their special immunity to the entities powers. Itas soon evident, though, that their involvement will be strictly limited. Are the hostages still alive? Can they rescue them? What are the entities planning now? Their next adventure into the unknown awaitsa]