In all the solar system there is no city quite like Mercis, capital of Mars. Solis, on Venus, is perhaps more beautiful, some cities of Earth certainly have more drive and dynamitism, but there is a strange inscrutable air about Mercis which even terrestials of twenty years' residence cannot explain. Outwardly a tourists' mecca, with white plastoid buildings, rich gardens, and whispering canals, it has another and darker side, ever present, ever hidden. While earthmen work and plan, building, re