While his grandfather was absorbed, Alex crouched to inspect the spring-heels. He picked one up. It was even heavier than it looked. After a moment, he sat and fastened the mechanisms around both feet, pulling buckles tight, then stood, testing the feel. His gaze fell on the moss-covered rock they had stopped beside. He tried a step, then hobbled heavily to stand before it. A broad boulder, about five feet high. Alex bobbed at the knees, trying to get a feel for the kind of force he might use to get up there.

He glanced at the old man’s back, took a breath, crouched, and jumped—then felt stupid when nothing happened. With the weighty apparatus around them, his feet barely left the ground. He frowned, then brightened, remembering the last little movement his grandfather had made, swiveling the heels toward each other.

“Must set the mechanism,” he muttered, licking his lips.

“Hmm?” his grandfather said over his shoulder.

At the same moment the old man turned and shouted—“Alex! No!”—Alex moved his feet quickly inward. Then something punched him so hard in the stomach that he couldn’t breathe.

XII.

OUT ON A LIMB

He still couldn’t breathe. He was beginning to panic about that. He couldn’t see, either. His eyes were streaming. The world was a gray-green smear, waving strangely up and down. Blood was rushing to his head. And possibly out his nose. He wheezed uselessly.

“Alex?” His grandfather sounded far away.

White spots sparked across his blurring vision. The weight pressing into his belly grew heavier. There was a jagged, tickling feeling there, too, as though something was struggling weakly, trapped against him.

“Alex?”

Trying to move away from it, he felt himself lurch forward and steadied himself by flinging out a hand, grabbing something rough. The agitation at his stomach was gone.

“Alex?”

Gulping fishlike, he finally found a shallow, shuddering breath. Then another, deeper. His vision cleared, but he couldn’t understand what he was seeing. To his right, an enormous gray pipe stretched off into a great greenish-brown wall, about sixty feet ahead. Something was waving oddly in the air nearby. Two things. Turning his head slightly downward, they seemed familiar. It took him a second to identify his own feet.

With sickening clarity, he realized. The gray pipe wasn’t stretching ahead into a wall. It was a tree trunk, and it was going straight down to the ground. The very hard ground. Sixty feet below. He was hanging bent double, flung over a high branch.

“Hang on, old chap, I see you now. I’ll get a rope from my bag.”

Alex opened his eyes and squeezed tighter to the branch as he felt himself slip. The weight of the machines around his ankles was dragging him back. His arms were beginning to ache. He didn’t know how much longer he could keep hold.