It had more slide and give to it than the confidently placed cobblestones and sleek pavement of the outer world. One more step forward, just to hear that telling crunch again, and Ahmad knew for sure.

“Sand,” he said.

Winnie reached down and let a handful slip through her fingers.

“It is!” she agreed, and then turned to him with wide eyes. “That is really weird, isn’t it? Isn’t the MasterMind all about the thick wires and huge sound effects?”

“Maybe this is another tug-of-war area,” Ahmad reasoned, though his mind wasn’t really concerned with this new development. They were now in the thick of the maze, and everything in his body felt that there was something important waiting here for them. Winnie’s words fell over him like an unwelcome rain shower pattering against a window.

The maze’s interior didn’t really give anything away. Apart from the constant light show and the sand underfoot, it was just . . . a maze. There was no writing on the walls, but there were arrows: large and as luminous as etched hieroglyphics on the side of an Egyptian pyramid, pointing every which way. They definitely wouldn’t be of help.

That persistent, low hum hung in the air too. Ahmad shook his head to clear it.

“What’s the rule about mazes again?” Ahmad broke into Winnie’s nervous pattering, raising the lantern to try and see down the nearest corridor. “We stay to the left, right?”

“I thought we discussed this back in that awful jungle challenge,” Winnie grumbled. “I’m no good with mazes. Hey, speaking of that, it’s weird. Why are we facing two mazes?”

“What’s wrong with that?” Ahmad decided on left and reached out to make sure Winnie was following behind him.

“Doesn’t the Architect like to mix things up? And the MasterMind seems to pride herself on not being predictable.”

“That is unpredictable, isn’t it? Another maze—unexpected. Look, Winnie, I’m trying to concentrate,” Ahmad started, and then stopped as the floor shifted under his feet. “Did you feel that?”

“No, no backtracking. What were you about to say?” Winnie crossed her arms over her chest.

“Winnie, I’m serious . . . Whoa!”

A real tremor shifted through the ground this time, enough to nearly unbalance Ahmad. He lowered himself to the ground.

“Do you think this is some sort of death trap?” Winnie asked anxiously. “Is it too late to mention that I’m not good with tight spaces?”

Ahmad had been doing well with not . . . well, being Ahmad. Now, though, he frowned and began, “Winnie, if you don’t—”

It took him a second to recognize that the rumbling had started up again, and now it wasn’t just under their feet. It was echoing down the corridors toward them.

Something was coming. And it was coming fast.