The rest of the weekend should have been filled with homework, but my mind was stuck on Mr. Snag and those slimes. The old ogre was as gentle as a granite sloth. There was no way he let the slimes loose. I didn’t have much to go on, but I just knew Snag was set up. My hunch didn’t make much difference though. By the start of the week, Tank and I still didn’t know what to do. And I still didn’t have my homework done.

To make things worse, we had gym class.

I don’t know who invented this part of our curriculum, but they should be dropped into the fire pit of the Howling Suck. I know, I know. Gym is great! Gym is fun! You get to run around. You get to scream. All good in theory. But when you have Rizzo Rawlins in your class and a gang of goons to back him up, gym becomes forty minutes of bangs, bumps and bruises. Even when I’m on the same team as Rizzo and the ogre twins, they still manage to bash, bang and bloody me.

Whoever invented dodgeball should be tossed into that fire pit too.

“Don’t sweat it, Fizz,” Tank said when I sat on the bench beside her. “Rizzo is just excited because his dad is taking them all on vacation next month.”

“Vacation? In the middle of the school year?”

“Yeah, he was bragging about it at lunch. His dad’s business is doing really well. Some big deal or something.”

The walls of the gym trembled.

“Here we go again,” Tank said. “Grab hold of something.”

The entire gym shook, sending kids falling to the ground. As soon as it came, the shaking stopped.

“It’s just the heater,” Ms. Blinx barked. “Get back into the game!”

“That’s the third tremor today,” Tank said. “They’re happening more often. Hope Mr. Zallin fixes the heater soon.”

“What exactly is wrong with the heater?” I put my hand over the heating vent behind our bench. “It’s not cold in here. And there’s hot air coming out of this vent.”

Tank wasn’t listening. She was on her feet, walking to the equipment room. I followed her.

“What is that doing here?” she said. She ran her finger through a pile of purple dust on the ground outside the door. “Interesting.”

She opened the door to the equipment room.

It was packed with balls, sticks, nets and other gym equipment. A line of purple dust trailed into the small room and disappeared behind a ball hockey net.

Tank stepped into the room. She pointed her camera at the trail and took a photo. I leaned down to get a closer look at the dust.

“It’s the same stuff as in Zal’s office,” I said.

The trail disappeared under an old hockey net. I tugged on it to get it out of the way. It wouldn’t move. But it did growl.

The little creature bounced around the room, screeching like I had stuck it with a knife. Hockey sticks clattered to the ground. Its sharp claws burst soccer balls and ripped crash mats as it jumped from wall to wall. All I saw was its tiny blue body scrambling into the heating vent.

Then the room was silent except for Tank’s heavy breathing beside me.

“What was that?” I said.

“I have no idea.”

The door to the equipment room flew open.

The whole class stood in the doorway. Dodgeball game forgotten. Rizzo Rawlins stood at the front of the pack.

“Figures the detective duds would trash the place,” he howled. “Just like their caretaker pal trashed the schoolyard!”

That got the whole class laughing. Ms. Blinx buzzed around behind them, telling them to stop and get back to the game. The kids drifted away, but the laughter didn’t stop. And our trouble wasn’t over.

A dark shadow fell over the doorway. Mr. Zallin’s large body blocked the light from the gym.

“Look at what you have done!” His deep voice boomed. His eyes blazed red. His whole face scowled. I’d never seen a caretaker so mad before. “You have destroyed school property! Principal Weaver will hear of this.”

In the caretaker’s face, I saw more than just anger. I saw something familiar. I just couldn’t place it.

As he marched us down to Principal Weaver’s office, I knew I had more to worry about than an angry caretaker. We’d just seen a creature that didn’t belong in our school. Something dark was happening here. I was determined to find out what. But first, I had an angry principal to face.