He seemed to think about that for a minute, then nodded. “That’s the best theory we have right now. Let’s assume that’s true and build our defenses accordingly.” He walked back to the door, then began looking it over. “The wards didn’t hold, huh?”

Scout shook her head. “Not even. Can you work it so they’re permanent? Like, they’d let Lily and me get through, but not anyone or anything else?”

Daniel pressed a hand to the door and closed his eyes in concentration. “Yeah, I could probably work that.”

It looked like he was getting started, but I still had a question. “Aren’t we going to go after them, or at least see how far they got? I mean, we can’t just let the rats run loose in the tunnels.”

He glanced back, only one eye open. “All the Adepts are accounted for, tucked safe and sound into their beds, with the exception of you two.” He didn’t say “trouble-makers,” but I could hear it in his voice. “So there’s no immediate risk. Not enough that would justify sending you out on a hunting mission.”

I couldn’t argue with that logic.

While Daniel prepared to fire up his ward, Scout sent a message to Lesley to let her know that her work was done for the night, and that we’d be up as soon as Daniel was done.

His method of magic was quite a bit different from Scout’s . . . or anything else that I’d seen. She’d said he was a protector. Maybe they had their own special brand of mojo. After he’d communed with the door, he pulled a short, cork-stoppered clear bottle from his jacket pocket and held it up to the light, checking it out. A white cloud swirled inside it, like he’d bottled a tiny tornado.

Daniel sat cross-legged on the floor, facing the door. He pressed his lips to the bottle’s cork, then pulled out the stopper. The mist rushed out. Daniel closed his eyes, smiling happily as it expanded and circled him, swirling around like a magical version of Saturn’s rings.

“What is that?” I whispered to Scout.

She shook her head. “I’m not sure.”

The rings still circling and his eyes still closed, Daniel put hands on his knees and offered his incantation. “Solitude, sacrifice in blackness of night. Visitor—enemy of goodness and light. Hear the plea of this supplicant, protector of right, and quiet the halls of this reverent site.”

For a second, there was nothing, and then the door flashed with a brilliant, white light that put huge dots in my vision. It took me a few seconds to see through the afterimages. By the time I could focus again, the mist was gone and Daniel had recorked the bottle.

Scout squeezed her eyes closed. “Little warning about the flash next time, Daniel?”

He stood up and put the bottle back into his pocket. The door’s glow faded back to normalcy. No buzzing, no pulsing, no vibrating rivets.

“That should hold,” he said, “at least until they find a work-around. As Adepts, you’ll be able to come and go at will. It’ll only keep out Reapers—and whatever else they try to drag in here.” He pointed toward the other end of the corridor. “That the way back to St. Sophia’s?”

Scout nodded, and we all headed off in that direction.

“What was in the bottle?” she asked as we took the stairs to the second floor.

Daniel slid her a glance. “You’ve never seen sylphs before?”

Scout pointed at his jacket. “That was a sylph?”

Surprisingly, I actually knew what a sylph was—or what it was supposed to be. My parents had given me a book of fairy tales when I was younger. There was a fable about three sylphs—winged fairies—who’d tricked proud villagers into giving the sylphs all of their youth and beauty. I think “Vanity gets you in trouble” was supposed to be the moral of the story. I always got the sense they looked basically like smallish people—not clouds of mist.

As if in answer to Scout’s question, Daniel’s pocket vibrated a little. “That was many sylphs,” he said, “and since I can still feel them rattling around, I think you offended them.”

They must have been snowflake-small to fit into that tiny bottle, I thought, wondering what else the underground had in store. What other creatures were hiding in plain sight, living among Chicagoans even though they had no idea?

“Sorry, sylphs,” Scout half shouted. “I didn’t mean to offend you.”

“You probably don’t need to yell.”

“Yeah, well, you’re not the one who offended the sylphs, are you? One can never be too careful.”

“I’d agree with that if I didn’t think you were being crazy sarcastic. I’m assuming you’re actually leading me out of this building?”

“Of course,” Scout said. “We’re taking the bad-girl exit.”

Daniel lifted his eyebrows. “The ‘bad-girl exit’?”

“Walk and talk, people. Walk and talk.”

Lesley was gone when we emerged upstairs, and the main building was quiet. Scout silenced Daniel with a finger to her mouth, and we tiptoed across to the administrative wing where the offices—including Foley’s—were located. “We’re taking the secret exit without the alarm. This is how some of St. Sophia’s busier girls, if you know what I mean, sneak in and out at night.”

“No way,” Daniel said.

Scout nodded. “Welcome to the glamorous world of boarding school. Where the things that go bump in the night are either horrific creatures—”