Sequel to Rockets in Ursa MajorFrom a great distance the Yela's recorded message crackled through on the micro-earpiece: 'For the time being you have won. But I am not defeated so easily.'That had been three years ago, after Dick Warboys had repulsed the invading Yela by firing a lithium bomb into the Sun. But now that threat seems near fulfilment as appalled scientists detect the rapid approach of a vast, engulfing cloud of hydrogen. Can humanity survive on Earth or must selected pioneers abandon it in search of a safer region of the Galaxy?To find the answer Dick and his allies from Space suffer a perilous voyage into the realms that reach the ultimate in understanding the physical universe.