The five children and one dog went into the front hall, moving quietly so as to not alert Baines. Colin led the way, and Amelie kept track, while Kat took notes on what they could follow and read.

“Look,” said Isaac when they reached the second floor near their rooms, where Colin thought the words began. “Can you see that?” It looked as if the drawing came to life, shimmering in the air around them, moving from the scroll to the walls themselves.

“Wow,” whispered Leo.

“This way,” said Colin, following the coiling form of the words that were revealed in order with every step they took. He read the words aloud and Kat transcribed.

Dear Isaac, Well done.

You’ve got the watch, the map, and the knife . . .

“Wait,” Isaac said, halting. “I don’t have a knife.”

“Maybe that’s what you were supposed to find in the ring of stones,” said Amelie. “I seem to remember reading about an iron knife that could render the Unseelie fae a mortal blow. I’ll have to look that up.”

“Assuming you can get close enough to an Unseelie,” Leo observed. “Which you might not want.”

“Then I’m missing a possibly important weapon,” Isaac said. He remembered then that his fingers had felt a niche in the stone where he stood inside the ring. He wondered whether that niche held the knife he should have found. He shook his head. He should have been more careful. Next time, he promised himself, he would be. Except, that was twice now. The knife, and Hypatia. He bit his lip as Colin continued reading.

What we do is guard magical artifacts that could be used for good or ill. The hunters seek what we hide.

They were walking along a windowless corridor, and Colin led them through a door, and down a narrow flight of stairs, a twisting, winding staircase. The blue-white shimmering in the walls that corresponded to their path on the scroll was the only light.

This map will take you to something that’s been hidden for centuries. Something you can use to help you uncover the next clue. Remember that if any of these artifacts land in the enemy’s hands . . .

“Wait,” Isaac said, stopping again. Now they were deep inside the castle, on the landing of the stone staircase. It was gloomy and cold. “Artifacts. That is the clue.” Colin took a few more steps.

. . . it will be dangerous for all humans.

“Whoa,” said Leo. “That sounds pretty bad.”

“Um,” said Colin, “it looks like the words end here.” He opened a door into a long wood-paneled room that was barely lit by windows at one end. “I think we have to look for whatever will help uncover that next clue in this room.”