“Whatever it is you’re selling, I don’t want it!” Mr. Trellik snapped.

The old troll was the color of slug soup. Steam drifted up from the tiny teacup in his large hand. One fact about Mr. Trellik—the old troll loves his tea. Mr. Trellik’s eyes nearly popped out of his bald head when he saw the massive slime at the bottom of his stairs.

“My mailbox!” he shrieked. He marched down the stairs, shaking his teacup at the slime. “You filthy brute! How dare you eat my property!”

“Careful, Mr. Trellik!” boomed a deep voice from the other side of the street.

Mr. Snag, our school caretaker, ran across the road. He carried a long toolbox in his big hands. The large ogre was out of breath. His round belly heaved in and out. It looked like a mud ball getting pumped up and deflated over and over again.

“My slimes ain’t filthy,” Mr. Snag said when he caught his breath. “Don’t be hurting their feelings.”

“Feelings!” Mr. Trellik spat. “These blobs are barely alive. They certainly don’t have ears, and I doubt they have feelings.”

“That might be true, but you don’t have to go and say it. Besides, my slimes can’t resist the taste of such high-quality brass.”

Mr. Trellik took a sip of his tea, considering Mr. Snag’s words.

“I do only use the finest materials.” He narrowed his eyes. “Don’t you butter me up, you old ogre! Get that slime off my mailbox before I call the police!”

Judging from the sirens in the distance, the cops were already on their way. Mr. Snag’s large ears drooped down the sides of his hairy head like a pair of sad wings.

Poor Mr. Snag. He was always cleaning up other people’s messes. He got your ball down when an older monster roofed it. He unblocked the toilet when Rizzo Rawlins and his goons jammed it with toilet paper or some unlucky first-grader. This mess was different. All caretakers in Slick City need a license to use cleaning slimes. There are strict laws on who can control slimes. In the wrong hands or left to slurp around on its own, a slime could cause a lot of damage. My school’s dissolved playground was proof of that. And so was Mr. Snag’s worried face.

Mr. Snag was in charge of the slimes at Gravelmuck Elementary. He watched over them like they were his own children. This mess was his mess.

The ogre pulled a small glass cube out of his toolbox. He tapped the cube. It hummed and grew bigger, until it was the size of a backpack. When it had finished growing, Mr. Snag held a solid-looking glass box. One side of the cube opened like a door.

Mr. Snag held the glass box closer for us to see. “This ain’t magic,” he said. “It’s the finest in trollish engineering.”

Tank’s troll ears perked up. She was an aspiring engineer. To her, Mr. Snag’s boxes were like candy to a double-mouthed sugar sucker.

“Are those sunken pistons?” she said.

Mr. Snag grinned. “And invisible gearing. A machine so perfect, it beats magic in every way.”

Mr. Snag placed the box on the ground beside the blob. He reached into one of the many pockets on his red coveralls and pulled out a small piece of dark stone.

“Obsidian.” He winked. “Slimes cannot resist the taste of obsidian.”

He dropped the obsidian pieces into the box. Immediately, the slime oozed toward the black stone.

“Can it smell it?” I said.

Mr. Snag shook his head. “Slimes don’t have noses, Fizz. They feel the vibrations of stones. It’s like they can hear rocks. And when they hear obsidian, they come slurping.”

The slime totally forgot about Mr. Trellik’s brass mailbox. It poured itself onto the obsidian and into the glass box. Amazingly, the box was able to hold the entire slime’s body.

“Another feat of engineering.” Mr. Snag grinned. “Tiny pistons in the box’s lining massage the slime and make it shrink to fit in the box.”

He pushed the lid closed with one large foot and picked up the glass box. Inside, the slime happily devoured the chunk of obsidian like it was a candy-coated rock bug.

“Won’t the slime’s acids just eat through the glass?” I asked.

Mr. Snag’s large ears wiggled with delight. “That’s the beauty of it! The glass is actually made from refined slick.”

“The goop sucked up from under the harbor?”

“The very stuff,” Mr. Snag said. “Slimes can’t stand the stuff, so they don’t eat it.”

The slime’s body squished up against the glass of the tiny box. Already, the piece of obsidian was smaller.

“Impressive,” I said.

Mr. Trellik snorted. “I’ll be more impressed when these beasts are gone from the front of my shop! I have a very important shipment coming today. I cannot have slimes here to greet my customers.”

The old troll pointed to a poster hanging beside the door to his antique shop.

“Firebane!” I said. “The dragon from the Dark Depths?”

“The very one.” Mr. Trellik grinned. “He has come upon hard times and chosen to sell off some of his estate.”

“You mean, ill-gotten loot,” Mr. Snag said. “That old dragon has terrorized the good people of Rockfall Mountain for centuries.”

“That is not my place to say.” Mr. Trellik shrugged. “I’ll have the wealthiest monsters from all over Rockfall Mountain visiting my store this weekend. Slimes are not invited!”

I peeked inside his shop. The place was packed with old furniture, parts of ships and display cases of gems and jewelry. The floors were black as the Dark Depths and polished to a shine. I’d never been inside, but it looked like a fun place to get lost. If Mr. Trellik wasn’t around, that is.

“It’s a good thing the slimes didn’t get a look at the floor inside the shop,” I whispered to Tank.

“Obsidian,” she said. The floor tiles of Trellik’s shop were made of the slimes’ favorite treat. “You can’t cut through that stuff. All the banks are built out of it. It is expensive, but very secure.”

“And delicious if you’re a slime,” I said.

A shadow fell across the front of the antique shop. A voice bellowed from above.

“Do not panic!”

“You’re making a big mistake!” I shouted. Not like that was going to stop the police from stuffing Mr. Snag into their car.

“You’ve got the wrong ogre!” Tank said.

Something was definitely wrong. I felt it right down to my tail. And a good detective knows to listen to his tail. I ran down the steps to the police car.

“Mr. Snag loves his cleaning beasts,” I said to the cop holding the car door open. “He would never let them escape like this.”

“That’s nice, kid.” The cop smiled like I was some first-grader bragging about losing a fang. He pushed Mr. Snag into the backseat of the car. “Your caretaker has keys to both the slime cages and the front door of the school. We know what we’re doing.”

“Zip it, Osborne!” A large ogre in a rumpled overcoat came around from the other side of the car. He looked like he washed his face in lemon juice. “This is a police investigation, not show-and-tell with the kiddies.”

Osborne’s grin vanished. “Sorry, Detective Hordish.”

Hordish turned to us.

“Keep your snouts out of my investigation, kids.” He waved Tank and I away with a big meaty hand. “Now run along. I’m sure you have homework to finish.”

Hordish and Osborne climbed into their police car. Mr. Snag stared out at us through the back window.

The caretaker’s long ears hung down the sides of his hairy face. His large eyes stared out at the school he had taken care of since before Tank and I were even born. Slime damage was everywhere—cars dissolved, fences melted away and the playground filled with puddles of slime acid. It was a mess, and Mr. Snag was going to take the blame.

The police car roared to life and sped downtown to the police station.

“This ain’t right, Fizz,” Tank muttered through gritted teeth. “Mr. Snag would never hurt the school or his slimes like this. We have to do something.”

“We are,” I said. “We’re going to find out who really released the slimes.”