Why has Roger Manning suddenly gone dark? Can his pal Tom Corbett really be dead? What caused the strange trouble on Titan—and how is it connected to a rocket race in outer space? These are but a few of the mysteries confounding Captain Steve Strong and the big Venusian engineer, Astro, as the Solar Guard races against time to save the mining colony on Saturn's largest satellite. At stake are the lives of hundreds of men, women and children; the future of the intrepid Polaris crew; and quite possibly the fate of the entire star system. Book 6 in Tom Corbett, Space Cadet series.