out!” she cried, stepping away from the wall.
They all froze, spinning from corner to corner, waiting for one side of the classroom to sprout spikes and begin marching toward them.
Nothing moved.
“Huh,” Kevin said, staring at the back wall. “Maybe the mechanism broke?”
“I can still feel the floor rumbling,” Persey said. Which meant something was happening behind the scenes.
A low hiss whistled above the hum of the faraway motor, followed by another and another. Four small white clouds erupted from the floor, billowing up from unseen spouts.
“They’re going to gas us!” Mackenzie cried. She pulled the neckline of her off-the-shoulder shirt up over her nose and mouth, muffling her voice. “It’s poison or something.”
Riot stepped closer to one of the clouds, which was thickening with every passing second, appearing significantly more opaque as it grew. He sniffed, then stumbled back, his body racked by a fit of coughing.
“See?” Mackenzie climbed on top of a desk, trying to stay above the white clouds.
“Not. Poison,” Riot sputtered. Then he flipped the collar of his shirt up and held it over his face, just as Mackenzie had done. “Chalk dust.”
Neela stared at the advancing cloud. “Standard classroom chalk is made from calcium carbonate, which is considered nontoxic, though prolonged exposure to the dust has proven to be a mild irritant and may complicate previously existing respiratory conditions.”
“So it won’t kill us,” Kevin said.
Nonlethal chalk dust seemed like a wasted opportunity to knock off another competitor. So far, every detail of the rooms had been meticulously planned: the designer had been one step ahead of them at all times. So why this innocuous school supply? What did it signify? Or what was it meant to hide?
“Look through the desks,” Persey cried as she raced to join Neela at the chalkboard. “See if you can find any other clues before we’re blinded by this stuff.”
Kevin set on the nearest desk while Riot headed to the exit door. Persey could just make out his figure through the thick cloud of dust as he examined the touch pads affixed to the door.
But while they were both working to find the solution, Mackenzie stood firmly on her perch, shirt still clutched around her mouth. “I’m not going anywhere until that door is open.”
As much as Persey wanted to table-flip the desk with Mackenzie still on it, she didn’t have time. Neela was transfixed by the chalk, probably trying to work out the mystery of its purpose when she needed to be working on a different problem altogether.
Persey grabbed Neela by both shoulders, physically turning her back to the math equation. “How fast can you solve for x?”
Neela blinked rapidly, refocusing as she scanned the chalkboard. “Um, a minute or two? But I have no idea what those are.” She pointed to the numbered chalk dots that were scattered seemingly at random to the right of the equation.
“Leave them to me.”
Neela nodded, then attacked the equation.
“Eight to the x over two to the y. Yes, definitely advanced exponent rules.” She muttered to herself as she started to work out the answer. “I’ll just rewrite this side of the equation, then substitute two to the three-x power for eight to the x…”
It was like number-and-letter salad to Persey, and while she marveled at Neela’s ability to see that jumble as a sentence to be diagrammed rather than a nonsensical collection of symbols, she didn’t have time to watch the magic unfold. The numbered dots presented another challenge. One they also needed to solve.
“It’s like a microcosm of Y2K over here,” Kevin said between coughs. His voice came from the back of the room, but the chalk was so thick, Persey couldn’t see him. “Lizzie McGuire notepad, tattoo choker necklace, Pokémon packs, Quidditch card game. Too bad Arlo isn’t here to nerdsplain how to play it.”
“Dude…” Riot said.
“What, too soon?”
“All your jokes are too soon,” Persey said, without pulling her eyes away from the chalkboard. She could still see it clearly, but even the few inches of space between her and it were now clouding over with whiteness.
“OW!” Riot yelped. Out of the corner of her eyes, Persey saw him jump away from the door. “That thing fucking electrocuted me.”
“The door?” Mackenzie asked.
“The lock.”
Persey joined him, peering closely at the line of number locks. “Which one?”
“Bottom.” Riot shoved his fingers in his mouth like a teething infant. “I barely even laid a finger on the number pad.”
A creaking hinge signaled that Kevin was searching another desk. “Any luck with those dots?”
“Then we