I was lying on the underside of the swamp—the reverse side of the muddy plain I’d just been tramping through. Gravity had turned upside-down. If I looked down I was looking up through the puddles at the blue sky of Fillory. If I looked up there was only darkness overhead. It was nighttime in the world under the Northern Marsh, and before me, across a flat plain of black mud and sun-filled puddles, was a fairy castle made of black stone. Its towers pointed down instead of up, but so did everything, including me.

This was new. Martin had taken us somewhere truly strange. Fillory was a land of wonders, but this place had an uncanny quality that I can only describe as not correct. It was a place that shouldn’t have been, somewhere off the edge of the board, where you weren’t meant to put a playing piece down. This wasn’t an ordinary adventure, another legend in the making. I knew already that Plover would never hear about it. This was happening off the books.

I could have turned back, but I knew that if I did I would never have a brother again. I also knew that what was happening to him would happen to me too. I would have two more years, three at the most. I didn’t want the game to be over yet. I’ll follow behind Martin at a safe distance, I thought, and watch what he does. Maybe he’s found a way out of the maze.

I stood up, fighting vertigo. Martin was waiting for me in front of the great door to the castle. He was sopping wet and smiling, though a little sadly I thought. I picked my way toward him, avoiding the puddles.

“This is it,” he said. “Just like they said in the books, but it’s different when you really see it.”

“Like who said? Martin, what is this?”

“What does it look like?” he said grandly. “Welcome to Castle Blackspire.”

“Blackspire.”

Of course it was. It was just the same as Whitespire, stone for stone, but the stones were black, and the windows were empty and dark. It was Whitespire upside-down and backward and in the middle of the night, the way it must look when we were all asleep and dreaming. Martin pulled his sopping sweater off over his head and dropped it with a smack on the smooth stone.

“But who lives here?”

“I’m not sure. At first I thought it might be backward versions of us. You know—Nitram, Trepur, that sort of thing. What’s Fiona backward? I can’t do it in my head. And we’d have to fight our opposite numbers to the death. But I’m starting to think it’s not like that at all.”

“Well and thank God for that. What is it like?”

“I don’t know,” he said. “Let’s find out!”