Ayla heard Crier asking a question—something about the Tarreenians—but she wasn’t paying attention. She was watching the boy hunched over the chunk of blue stone, holding it steady for his hammer. As she watched, he tapped away at the same spot one, two, three times, until the stone split in two, shards falling away like pieces of eggshell. She stepped closer still so she could see what the other boy was carving. Not letters. Symbols. Ayla recognized fire, saltpeter, sulfur.

A thousand times more powerful, more potent, than heartstone.

Ayla could be wrong, but she knew in her heart—in her blood—that she wasn’t. She had seen this blue stone before. She’d seen it in Siena’s hand, as Siena lowered it into the open chest of a lifeless Automa girl, fitting it into the hollow space where a heart should be. Ayla still remembered how the girl had twitched as if struck by lightning, eyes flying open. Irises burning silver.

Creation. Destruction. A heart and a bomb. The reason Kinok had brought her to his study and interrogated her about her family’s past.

Tourmaline.

Here it was.

“How is it so much more powerful than heartstone?” Ayla asked. “Aren’t they both just . . . rocks? Crystals?”

“Oh, but that doesn’t mean they’re the same. Crystals have different properties. Sulfur burns, phosphorus glows, chalcanthum dissolves in water. You feed coal to a hearth fire. You feed heartstone to an Automa.” The nearest shelf was lined with leather pouches the size of a clenched fist. Dinara fetched one of the pouches and held it in her palm, giving Crier and Ayla a significant look. “It all depends on what you do with the crystal, with that materia, doesn’t it?” she said. “Cinnabar is used as both poison and pigment. Inhale cinnabar dust and you’ll die slow and nasty, but you can turn that same dust into the most beautiful vermilion paint. It can take your last breath; it can breathe life into art. Alchemy isn’t the only way of manipulating a substance to serve one purpose or another, to create or destroy. It is not the only magick.” Her lips curved up again, a natural smile. “It’s the magick we’re using, though.”

“You’re harnessing the energy,” said Crier. “Generating magickal energy by carving those symbols into the stone. Like . . .”

“Flint and steel,” Ayla supplied. “Is that it? The blue stone is the flint, and if you have the right combination of symbols, it’s like striking flint against fire steel. Except it doesn’t make fire, it makes—like Crier said. Energy. That’s how the Makers create heartstone, right?”

For some reason, Dinara’s smile slipped. “That’s what we thought,” she said. “But—”

“Boss?” the boy with the hammer piped up. He was frowning, holding a lump of Tourmaline up to the lanternlight. “Can you come look at this? I can’t tell if this vein’s gonna be a problem or not.”

“One moment,” said Dinara, then pressed the leather pouch into Ayla’s hands. It was heavier than Ayla might have expected, like whatever was inside was as dense as solid lead. “Take this. Just in case.”