CON-FEN By JAMES R. ADAMS _The Shisti and the Assistant Shisti of Mars chose Chicago, U.S.A., for their vacation spot. No worries; they were invisible. Plenty of rich food; the joint was loaded. A whole year of frolicking in store. Only one thing they overlooked--there was a curious convention going on._ [Transcriber's Note: This etext was produced from Planet Stories May 1953. Extensive research did not uncover any evidence that the U.S. copyright on this publication was renewed.] The landing on the green planet, Koosh told himself in satisfaction, was one of utmost perfection. Not that that made it unusual, since the Martian craft all but handled itself and invariably performed almost one hundred per cent flawlessly. But Koosh did feel that this landing was a little, just a little, better than average, and his ability as pilot had made it so. Thuko apparently thought the same, for he touched the other on the back of the neck in brief compliment. Twirling his eye-stalks in pleasure, Koosh pressed a button on the control panel and arose to follow Thuko to the opening airlock, hopping on one leg, which happened to be all that he or any Martian possessed. They emerged into warm, late summer air. For a moment they stood, filling their lungs, reveling in the rich, heady atmosphere that was so unlike their own. "Wonderful, Thuko!" Koosh enthused. "And to think we have a full year of it ahead of us!" "You are no less pleased than I," Thuko agreed. "But we must take care that nothing happens to the ship in that time. Loss of it would mean the end of all this." He did not need to mention the reason. Koosh knew that it was because the small craft was the only one in existence. At least, as far as Mars was concerned. And of course that was because--well, actually it was not a Martian ship. Thousands of years ago a lone, exploring Jovian had landed on Mars. After brief inspection of the machine, the Martians had decided it was a thing much worth having. They promptly murdered the Jovian, thereby neatly solving the problem of how to gain the gleaming silver sphere for themselves. Operation of the ship had proved only a matter of learning the right buttons to push. And the Martians were more than capable of making the few simple repairs it required from time to time. But they were stumped completely by the anti-gravity plates that drove it. All attempts to duplicate them had ended fruitlessly. The original would have to serve them until another Jovian came. "Where shall we put it for safekeeping?" Koosh asked. Then, answering his own question, "I imagine a likely place would be on the roof of an unoccupied building in whatever city we choose as our initial--ah--host." "That is a good suggestion," said Thuko. "A rooftop would be ideal. Let us proceed to find one in a suitable metropolis."