Whirling silently through space, satellite cameras pick up a suspicious new Soviet missile complex which at all costs must be properly identified. The mission is carefully planned and carefully rehearsed. The latest and the fastest MiG, which a defecting Soviet pilot has conveniently landed in the West, is to fly at a treetop level until well into Soviet airspace and on course for the target. And the return journey? Well, that's up to Quiller.