She found the chamber on a Wednesday.
Not the archive, not the central space, she wasn't that close yet. But the sub-basement of the building on Grain Street, the one with the pre-Sovereign foundation wall he'd been careful to keep her attention on, had a secondary space she'd apparently found by being thorough in the way Mei Sulan was thorough about everything.
He knew because she came to his stall that afternoon with the expression of someone who had found something that had shifted their understanding of the problem and was currently deciding what to do with the shift.
She didn't say any of that. She bought dried silvergrass, the correct amount at the correct price, and stood at his counter for slightly longer than the transaction required.
"The sub-basement has two levels," she said, not looking at him.
"Does it," he said.
"The second level has formation work I can't date. The style is unlike anything in the current reference catalogs." A pause. "I've sent a description to the Assembly's historical formation archive for comparison. I expect a response in five to seven days."
He processed this with the part of his mind that was always running the threat model. Five to seven days. She'd find a partial match at best, the Assembly's historical archive wouldn't have pre-Sovereign reference material because the Assembly had spent three centuries making sure it didn't exist in accessible form. But a partial match would tell her the formation work was old. Very old. And that would narrow her search considerably.
"That sounds like a significant find," he said.
"It is." She looked at him now. Direct, the way she did when she'd decided something. "There's also a qi signature in the second level. Faint. Distributed in a way I haven't encountered before." She paused. "No single point of origin."
He kept his face at helpful-confused. "What does that mean?"
"I'm not sure yet," she said. And that was honest, he could tell, the specific quality of her honesty that showed up when she was talking about something she was still working through rather than something she'd already concluded.
She picked up the silvergrass. She didn't leave.
"The people in that building," she said. "The ones who were evacuated. Two of them reported feeling disoriented in the weeks before the evacuation. Difficulty sleeping. A low-level buzzing sensation they described as coming from below."
"The formation disturbances," he said.
"Yes." She looked at the herbs on his counter. "And no. The disturbance pattern has changed in the last week. It was periodic before, consistent intervals. Now it's steadier. Lower frequency. Like something that was intermittent has become constant."
Because he'd told the archive to settle. He'd modulated it to protect people and she'd felt the change.
She was so good at her job it was genuinely inconvenient.
"Should the residents be concerned," he said.
She looked at him for a long moment. "I don't know yet," she said, which was also honest. Then she left with her silvergrass and he watched her go and thought about five to seven days and what he needed to do before the Assembly's historical archive sent her something useful.
He needed to move faster.
He went to find Rou.
End of Chapter 18