The air opened out before him, raggedly framing a bright-lit three-dimensional picture. He was staring down across a foaming river to the rim of a towering green and yellow forest. The crash of the river filled the building. Something bulky and black at the far left ... but the scene was gone-- The interior of the laboratory building lay quiet and unchanged before them again. Dowland said hoarsely, "How did you know what was going to happen?" "I was in a position to spend several hours observing it," Trelawney said, "from the other side. You see now, I think, that we can put your mountaineer's kit to some very practical use here." Dowland glanced across the building. "The walls...." "Metasteel," Trelawney said, "and thank God for that. The building's sound; the stresses haven't affected it. We'll have some anchor points. A clamp piton against that wall, six feet above the console walk and in line with it, another one against the doorframe here, and we can rope across." Dowland saw it, unsnapped his harness, fed the end of the magnerope through the eye of a piton, and twisted it tight. "Are we going together?" he asked. Trelawney shook his head. "You're going, Dowland. Sorry about that, but this is no time for sporting gestures. The rope doesn't eliminate the danger. But if you find your feet suddenly dangling over the air of a very old time, you'll still stay here--I hope. If you don't make it across, I'll follow. We get two chances to shut Ymir down instead of one. All right?" "Since you have the gun, yes," Dowland said. "If I had it, it would be the other way around." "Of course," Trelawney agreed. He watched in silence then as Dowland rammed the threaded piton down the muzzle of the gun, locked it in position, took aim across the machine platform, and fired. The piton clamp made a slapping sound against the far wall, froze against it. Dowland gave the loose end of the rope a few tugs, said, "Solid," cut the rope, and handed the end to Trelawney. The Freeholder reached up to set a second piton against the doorframe, fed a loop of the rope through it, and twisted it tight. Dowland slipped a set of grappling gloves out of the harness, pulled one over his right hand, tossed the other to Trelawney. "In case," he said, "you have to follow. Magnerope gets to be wearing on bare hands." Trelawney looked briefly surprised, then grinned. "Thanks," he said. "Can you do it with one glove?" "No strain at that distance." "Too bad you're not a Terran, Dowland. We could have used you." "I'm satisfied," Dowland said. "Any point in waiting now for another run of those cracks in space before making the trip?" Trelawney shook his head. "None at all, I'm afraid. From what I saw, there's no more regularity in those stress patterns than there is in a riptide. You see how the rope is jerking right now--you'll get pulled around pretty savagely, I'd say, even if you don't run into open splits on the way across."