Mercury, too, had certainly been mixed up with that violent past. And now it hovered, a disturbing enigma, in both the immediate and the farther future. In only moments, now, that past would blend with the present. His--Rick Mills' present. Fane would be in it, too. With the brassy taste of worry before the nameless in his mouth, Rick realized how easy it might be to be unjustly suspicious. So he tried to fight off his tension, which most of his companions must share in some degree. He tried to substitute an adventurous eagerness. Amid gusts of fire from its underjets the _Sun Child_ thudded down at the old Martell campsite in Mercury's Twilight Belt which rings the planet between its hot and cold hemispheres. Here there is day and night of a sort. For Mercury, wobbling a little in its eccentric orbit, does not always keep exactly the same face turned sunward. In the Twilight Belt the sun sometimes rises slightly above the horizon, and then sinks back. Here there is no terrible heat or cold. Everything was done now with swift precision. Like establishing a beachhead in some Earth-conflict of years ago. These five hundred men of the Survey Service, though civilians, functioned like a small army. They were the vanguard of research workers that must spearhead the occupation of yet another world. Bookish and academic they might seem, but they were trained for great ruggedness, too. Working in space suits, they strung a security perimeter of electrified barbed wire around the ship. Breastworks were built and weapons were mounted against the unknown. Air tight tents to house testing instruments were set up and inflated. Everyone--Rick Mills, Lattimer, Turino, Finden, Schmidt, Horton, and the hundreds of others--toiled hard. * * * * * Then there was time to really look around. The dry rusty plain bore patches of low vegetation, with crinkly, silver-gray whorls. Lichen, it looked like. A sad remnant of life. In the all but airless sky stars blazed, even though a white-hot silver of the sun peeped above the brooding horizon, beyond which, for all one knew, great metal shapes might hide, waiting, preparing an ambush. Nostrand, the leader of this expedition, held an aneroid barometer in his gloved hand. He was gray as iron, square-built of face and body, with widely separated teeth. He grinned, now, and spoke through his helmet radiophone: "Funny. There's a wisp of air left. Small as it is, and with a gravity only one-fourth that of Earth, Mercury shouldn't have been able to hold down much of an atmosphere for more than a few thousand years. It should be as dead as our moon by now. A minor riddle, eh?" Nostrand's tones fell, almost unnoticed, into a hollow stillness. Fane was standing near. He said nothing, but Rick Mills saw him grinning like a Cheshire cat.