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.

The room was big enough, maybe fifteen feet square. Rough shelves lined three of the walls and held a collection of treasures—literally in some cases. A bird’s feather was displayed next to an elaborate silver crown studded with cabochon gems set in silver flowers and vines. In a world where you were mostly alone, the feather was as valuable as the crown. There were books, too, but not very many—none that I could have read.

On the fourth wall there were a pair of wardrobes. The first was itself a work of art. Every bit of the wardrobe was elaborately carved in abstract designs. The second, like the walls of the tree house, was cobbled together out of bits and pieces of other things.

“I’ve never had anyone in here,” Aiden told me. “I built this after most of the others were already dead.”

“It’s charming,” I told him, seriously.

“Aboveground gives you a lot of protection,” he told me. “The first one I built here had windows—that was a mistake.”

He opened the elaborate wardrobe and pulled out some thick rag rugs and threw them at random on the floor. “I sleep . . . slept on piles of these,” he said. “We can use the bedrolls, but the rugs will soften the floor.”

“Sounds good to me,” I told him. In lieu of speech, Adam stretched out on one of the rugs and rested his muzzle on his front legs. “Adam approves, too.”

“I might as well get the artifact,” he said, and opened the second wardrobe. As soon as the doors separated, I could feel a wave of power.

The wardrobe was split into two halves. The right half had shelves filled with bright-colored fabric bags of all sorts of sizes and colors, with small boxes of bone, wood, or lacquer, and larger, jewelry-box-sized boxes. The bottom shelf was full of folded cloth. The left side held staves and swords and pole arms of all kinds.

“Are these all artifacts?” I asked.

He nodded. “I keep them in this wardrobe because it doesn’t let the power leak. Around here, power attracts attention.”

“When the fae come back,” I said slowly, “could someone find your house and your treasures?”

He shook his head. “Once a place belongs to you, it belongs to you. No one will ever be able to find this place unless I’m with them. No one can come inside unless I invite them in. It’s how Underhill was set up—and even she can’t change the rules. That’s why, even though she’s mad at me, she couldn’t actually make us wander for long before I found my home. If I die, Underhill will reclaim what is here. She has her own treasure rooms—I’ve seen them. Some of this stuff comes from there.”

I looked at the contents of the wardrobe. “Don’t ever tell anyone this is here,” I told him. “The fae would never have let you go if they knew what you have.”

He nodded, reached in to the shelves, and brought out a small box and opened it. The box he put back on the shelf. In his hand was a crude bronze key. He gave it to me, then closed the doors of the wardrobe.

The key was warm in my hands.

“What does it do?” I asked.

“Pressed against a door, it makes any door a gateway to Underhill,” he said. “If you keep in mind where in Underhill you want to appear, that doorway will take you there.”

“How do you know that?” I asked.

“Underhill isn’t opposed to sharing knowledge,” he told me. “Not if she’s in a good mood.”

He looked unhappily at the key in my hand, and thinking he was worried I wanted it, I handed it back to him. But, though he closed his hands on it and stuffed it in a pocket of his jeans, the scent of his unhappiness didn’t change.