Something roared, and I had the feeling that my ears weren’t picking up the whole thing—as if some of that roar wasn’t just sound. Skittering sounds came from the walls and the ceiling. There were no windows in the tree house and part of me was grateful. Whatever was making that noise sounded like a thousand rats or something with a thousand legs. Most of me hated hearing a threat I could not see.

Adam snarled.

“You lost,” said Aiden again. “This is doing you no good. If you don’t leave, I’ll light my wards.”

That horrible aching roar traveled through the walls and into my skull, sending hot pain through my nervous system.

“I warned him,” said Aiden. “He should know better.”

He pressed his hand on the door and . . . his magic wasn’t as big as what Beauclaire had used on the bridge, but it was plenty big enough to make me sit down on the floor harder than I’d meant to. There was a whoomph sound, like when a gas burner is turned on—only an order of magnitude bigger than that.

Silence fell.

Aiden took his hand from the door and shook it. “It won’t have killed him—not the flames nor the fall from the tree—but he won’t come up here again for a while.”

“What was that?” I asked.

Aiden shrugged. “I call him the Unseen. I don’t actually know what he is supposed to be. He’s one of the things that escaped from the prisons the fae left behind, and a lot of them started out as fae. He’s difficult to see except in strong sunlight. He’s slow, or he’d have killed me a long time ago.”

He looked around the room and blew out a huff of air. “Welcome to my home. It’s safe here—as safe as anywhere in Underhill. We can spend the night and look for a way back out tomorrow. The artifact is here.”

Now that we didn’t have unknown monsters trying to get in and eat us, I looked around. Without windows, the interior was dark except for a little light that snuck in between the hand-hewn boards—that looked more like they’d been scavenged than cut to build this tree house. The widths would be consistent for a section, then change. Right next to the door, there was a panel that was six or seven feet wide. Another plank looked more like a tabletop than a board.

Aiden lit some beeswax candles. Maybe if I’d been human, it would still have been too dim, but I see pretty well in the dark.