Bob Burke is a "lone castaway on Mars" after he survived a spaceship crash seven years earlier. Living in the Southern desert of Mars, he fashioned a shelter from the remnants of the spaceship. Food was plentiful, but Bob was lonely. His only friend was a Martian Gwud, "an ugly but alert creature" who followed Burke around like a faithful dog. The Martian Gwud is killed by one of the Scowling Mercurians after it let out a loud chatter to warn Princess Teba of danger as the Mercurians approached Burke's shelter.