If the universe is infinite, it follows that somewhere there may be real physical worlds that duplicate those of the imagination. And when Tom Carson caught sight of the third planet of 82 Eridani, he recognized at once its resemblance to that imaginary Mars called "Barsoom" of the ancient novelist Burroughs. Of course there were differences, but even so this planet was ruddy, criss-crossed with canals, and its inhabitants were redskinned, fought with swords, and had many things superficially in common with the fantasy Mars of the John Cater adventures. But there were indeed vital variations that would eventually trip up the self-deceived science-fiction-reading travellers from 24th Century Earth. Theirin hangs a tale that will delight and surprise everyone who enjoys the thrill of exploring a new world, especially one that seems peculiarly familiar.