“Hmmm?” His grandfather was working his other foot into the second device. “No. Well: yes. He built them—but I stole them, long time ago. Not used them in a while, though. Let’s see, good lord, must be sixty years. Last time was . . . down around Cannes. Ha.” He smiled distantly. “There was a masked ball, movie stars in town, a lot of jewelry, and . . . Well, it was a long time ago. Swore off them after that. But needs must when the devil drives.”

The old man stopped fussing with the apparatus and smiled up. “Thing is, Alex, I’ve been feeling a little . . . tired lately. Too much running around, I suppose. So I thought I might use these for a little help, if my energy gets low. Put a spring in my step, as it were. Ha. I had Albert tuning them up for me. Harry collected them while I was away.”

He stood, took a tentative step, frowned at the squeal it produced. He turned back to his Gladstone, found the oilcan Albert had given him, applied a few drops and pumped his foot until it was silent.

“Thought it best to get a little practice in. When I broke into the library back there, I overshot, wound up at a window a floor above. But I remember the real trick was walking in them. The jumping stuff’s quite easy, once you get the hang of it. The spring-heels multiply the force of your leap, basically. Although it gets a little exponential after a certain point.” He stood flexing his knees, looking upward and ahead. “Okay. Right.”

He crouched and swiveled his feet quickly toward each other, almost as if he were clicking his heels. Then he was gone.

Alex gawped at the spot where his grandfather had been. He spun, looked around, looked up, hunting the canopy overhead. He finally located him balanced on a branch about thirty-five feet up a tree around thirty feet away.

“That’s amazing,” Alex breathed. “That was amazing!” he shouted now, running to stand beneath the tree.

“I was actually aiming for the next one down,” his grandfather called, gesturing to a branch some ten feet below. “But, no, not bad after six decades. Getting down’s the real test. Stand back, please.”

Alex retreated, then caught his breath as the old man stepped casually from the branch. He fell tombstoning down, yet landed as though bouncing lightly on a mattress. The springs at his heels gave out a hissing sigh.

“Let’s see.” He crouched, creaked, and vanished once more in a gray upward blur, to land on the lower branch he had previously indicated.