Things were quiet that night in the space port. Then the 'Theban' arrived without warning, bringing with it a surly crew, led by a blustering captain, Larson... The 'Theban' was old, propelled by a totally obsolescent interplanetary drive. The only way Larson could get it off the ground was to kidnap the young engineer, Horn, who he hoped could at least manage to keep the ship in flight until it reached its final rendezvous. Their destination was the spaceship 'Danae' - a ship loaded with millions in space credit notes. If horn wanted to save the 'Danae' from the onslaughts of the Space Invaders, he had his work cut out for him...