In an alien spaceship hidden in a swamp near Collinwood, Roger Collins and his friend, space scientist Murdoch Gray, lie bound and gagged - yet no one even knows they are missing! For their captors are able to change shapes at will, and two of them have 'become' Roger and Murdoch. Although Elizabeth and Carolyn sense a difference, they can't guess that they are at the mercy of beings who will stop at nothing to prevent the next U.S. space flight under Murdoch's direction! Then, as the dark shadow of death draws closer to Collinwood, a bat soars over the hidden spaceship, flies close enough to see inside... and suddenly Barnabas and Quentin Collins find themselves joined in a desperate attempt to save Collinwood from the strangest menace it has ever known!