Calhoun made a wry face. He'd remembered something. Among the tales that had been carried from Earth to the other worlds of the galaxy there was a completely unimportant mystery story which people still sometimes tried to write an ending to. It was the story of an ancient sailing ship called the _Marie Celeste_, which was found drifting aimlessly in the middle of the ocean. There was food on the cabin table, and the galley stove was still warm. There was no sign of any trouble, or terror, or disturbance which might cause the ship to be abandoned. But there was not a living soul on board. Nobody had ever been able to contrive a believable explanation. "Only," said Calhoun to Murgatroyd, "this is on a larger scale. The people of this city walked out about three days ago, and didn't come back. Maybe all the people on the planet did the same, since there's not a communicator in operation anywhere. To make the understatement of the century, Murgatroyd, I don't like this. I don't like it a bit!" II On the way back to the Med Ship, Calhoun stopped at another place where, on a grass-growing planet, there would have been green sward. There were Earth-type trees, and some native ones, and between them there should have been a lawn. The trees were thriving, but the ground-cover plants were collapsed and rotting. Calhoun picked up a bit of the semi-slime and smelled it. It was faintly sour, astringent, the same smell he'd noticed when he opened the airlock door. He threw the stuff away and brushed off his hands. Something had killed the ground-cover plants which had the habit of killing Earth-type grass when planted here. He listened. Everywhere that humans live, there are insects and birds and other tiny creatures which are essential parts of the ecological system to which the human race is adjusted. They have to be carried to and established upon every new world that mankind hopes to occupy. But there was no sound of such living creatures here. It was probable that the bellowing roar of the Med Ship's emergency rockets was the only real noise the city had heard since its people went away. The stillness bothered Murgatroyd. He said, "_Chee!_" in a subdued tone and stayed close to Calhoun. Calhoun shook his head. Then he said abruptly: "Come along, Murgatroyd!" He went back to the building housing the grid controls. He didn't look at the spaceport log this time. He went to the instruments recording the second function of a landing-grid. In addition to lifting up and letting down ships of space, a landing-grid drew down power from the ions of the upper atmosphere and broadcast it. It provided all the energy that humans on a world could need. It was solar power, in a way, absorbed and stored by a layer of ions miles high, which then could be drawn on and distributed by the grid. During his descent Calhoun had noted that broadcast power was still available. Now he looked at what the instruments said.