'Emergency computations seldom achieve absolute precision. And thereby hangs and exciting tale...What do the men of the space patrols think about as they chart their hazardous undertakings in the shadow of the Lunar Apennines or on the rust-red plains of Mars? What margins for error do they allow for air, fuel, food and water in calculations of hair-trigger accuracy on which their very lives must, of necessity, depend? You'll be in a far better position to judge when you've read this breathless F. B. Bryning yarn.'