Wollheim writes of a Mars that is, as a substantial section of planetologists believe, "A world wheron a planetwide irrigation project is revealed to the eyes of earth by a spidery network of pole-to-pole canals! In connection with this the question has always been raised as to why, if Mars is the abode of intelligent beings, they have made no effort to contact us? In this novel, I suggest one possible answer to this riddle".