We had only just stepped into the tunnel when the walls began to shake. Another tremor rocked through the school. Behind me, in Zallin’s office, tools rattled along his desk. Something heavy fell to the floor, landing with a loud crash. The shaking was much worse down here, but still there was no boom or loud noise.

“That’s the third tremor today,” Tank said. “That’s the most we’ve had in a day.”

The tunnel was longer than I had first thought. We trudged through the darkness without speaking.

I pulled the jar of slime out of my pack.

“Little Scrapper isn’t glowing,” I said. “I don’t think our slime radar is working.”

“Stop!” Tank grabbed my shoulder. “Did you hear that?”

Something heavy scraped along the tunnel behind us. We froze.

There it was again. Footsteps on stone.

Getting closer.

“Someone’s coming,” Tank whispered.