An explosion went off beneath him, but this time he was ready. For an instant, as he rocketed upward, Alex experienced a thrill similar to that which he had felt when soaring with his flier. His elation was whipped away on the wind as he realized he had been flung far too high. He saw the old museum dropping away beneath him. Then he was plummeting toward its roof, arms and legs windmilling wildly, trying to grab the air.

His flailing right foot hit first. Part of Alex’s mind briefly noted how the machine strapped around it acted to absorb the shock of the impact with a violent hiss. Then he was sent tumbling forward.

He hauled himself up, panting, surprised to find he could stand, and surveyed the strange terrain. The sky felt close and cool. City lights gleamed low around him. A section of peaked roofs stretched dimly away toward the new part of the museum. He searched for the best spot to land, gauging the distance, and tried to recall everything his grandfather had told him about the devices, which wasn’t much. Basically, the spring-heels multiply the force of your leap. Although it gets a little exponential after a certain point. . . .

A sharp hiss from behind announced the tall man’s arrival. Alex didn’t look back. He jumped.

This time he put less force into the leap. He told his body it was just like jumping over a large puddle in the road. As he sailed through dark air, a gust of wind caught the canvas at his shoulders, slowing his flight, dragging him back. He landed lightly, the heels sighed, and for a millisecond he was pleased with himself. But he had undershot. Now he was sliding backward down a slick slope of tiles, the edge coming up fast.

In frantic reflex, he stamped down hard with one foot, forgetting what would happen. The single spring engaged. The lopsided eruption sent him somersaulting high and helpless, heels over head.

His feet slammed down on another part of the roof, then flung him up again. He shot toward a sheer wall, curled instinctively, forcing his legs to lead, kicked and cannoned away. As he bounced like a rubber ball, the next few seconds were a jumble of rushing impressions. Walls and roofs, Stuttgart spinning, night sky and streetlights.

Some calm section of his mind was determined to solve the problem. In his desperation, he was trying to cushion the expected shock instead of just letting the heels do their work. That was his mistake. With a huge effort of will, he forced himself to surrender control. Suddenly, he was falling, straight down, but he hit the ground almost gently, the spring-heels exhaled, and he flopped forward onto his hands and knees, gasping.

Lifting his head, dizzy, Alex shrank from a group of tall people gathered around him. Then he realized they were statues.