“An artifact is an old object, of any kind,” Amelie said. “Jewelry. A sword. A mirror. A potion. But a magical artifact is infused with power. Some of the stuff of legends, like, you know, Excalibur. Or Aladdin’s lamp with the genie inside or the Chinese emperor’s nightingale. Other objects may have magic but no stories about them. Yet.” She paused. “A magical artifact can be just about anything.”

“Wait,” Isaac said. His mind was spinning. The casket and its contents. “Anything?”

Amelie nodded. “In the case of Kat, her artifact is a piece of jewelry called a chatelaine. The monster she used it on wanted to enchant all of us who were here then.” She stared away, at the gray mist outside. Then she said, “Kat didn’t believe in magic back then, at first, but thank goodness she found her gift before it was too late. It was a scary time,” Amelie ended in a whisper.

Isaac said, “That object she carries in her pocket, yes?” That powerful silvery object Kat carried that made Isaac’s head hum. “What happened to you?”

“It’s hard to explain,” Amelie said slowly. “The monster tried to enchant us children. There were a bunch of us here then, and it wanted to . . . It tried to steal our souls.”

“What!” Isaac couldn’t believe it.

Ame nodded. “It was such an awful feeling. Like being ripped into shreds. I was awake, but I wasn’t. It hurt horribly but it was also so, so sad. If it hadn’t been for Kat . . .” Ame set her lips in a thin line and shook her head.

Willow floated down in front of Amelie. “Want us to make some goofy faces to cheer you up?”

“What happened to the monster?” Isaac asked.

“Mostly it’s at the bottom of the well,” she said. “In bits and pieces. Good and gone.”

Mostly, Isaac thought.

“That’s right,” said Willow, and they contorted into the shape of a puffy cloud before making a distinctive noise that made Isaac want to hold his nose. “Good. And. Gone. In pieces.”

Isaac, gazing up at the wight, found his eye straying to the library’s ceiling that was decorated with designs. Colorful and intricate, they reminded him a little of the cathedral windows at home. Except that these were more elaborate natural images of trailing vines and peculiar fruits.

Isaac squinted and stood to see better.

The jumble of vines converged at four points, and at each convergence was a particular design. One that Isaac knew. He pressed his hand against his chest, the pendant cold against his skin, and that distant throb rose again in his brain, like the sea pounding the cliffs or a low, slow heartbeat.

“That,” he said, pointing.

“Oh!” Amelie turned and stared. “Why, isn’t that what you were telling us about last night? The eternity knot?”

He nodded. Monsters. Artifacts. The eternity knot.