He saw it again. It was not a hypership, nor even an ordinary air-jet. It was a jet-down. He could see the faint glow of the ion trails coming out of the vertices of a hexagon, neutralizing the gravitational pull and allowing the wings to keep it aloft like a large soaring bird. It was a vehicle that could hover and explore planetary terrain. ...

The jet-down was closer now, but it couldn't hide from him, either. The rumble of the engine gave it away and they couldn't turn that off, not as long as they wished to continue their search. Seldon knew the jet-downs, for on Helicon or any undomed world with skies that cleared now and then, they were common, with many in private hands. Of what possible use would jet-downs be on Trantor, with all the human life of the world under domes, with low cloud ceilings all but perpetual--except for a few government vehicles designed for just this purpose, that of picking up a wanted person who had been lured above the domes? ...