“But?” Theo prompted.

“How do wards in these two positions keep out a demon? Why didn’t she just come into the city somewhere else? Not through the gate but across the lake, or from Evanston. Couldn’t she have just walked into the city literally anywhere else?”

“Not very good wards if that’s the case,” Theo said.

“Exactly. They’d be really crappy wards.”

“Maybe they’re concentric rings,” Petra said. She opened a sweetener packet, drew a wide circle in white powder that intersected with the gate. “Cornerstone fuels the ward, and the ward is basically this big ring. So the ghosts appear wherever the demon pops up along that ring.”

“Okay,” I said. “That makes sense. Except for here.” I pointed at the lightning machine. “It’s nearly downtown. That’s a long way from the gate. If the wards are in concentric rings, why didn’t she trigger something in between?”

“Maybe it’s broken,” Petra said. “It’s been a long time since they were established. Maybe they didn’t all survive the intervening years.”

“Wouldn’t there be more than one, though?” Theo asked. “Otherwise, the gap is too big. And I think you’d only build a defense in rings if you’re protecting something in the innermost ring. Like a castle. Moat, wall, keep, et cetera.”

“There’s nothing that says Rose is targeting something downtown,” I said, “or what used to be downtown in 1872, anyway.”

“Maybe there are only two Cornerstones,” Petra said. “Imagine the planning and magic that would go into something like this.” She tapped a finger—which I just realized was inset with tiny gold stars—near the outer sweetener ring. “Maybe this was all the time or energy they had.”

“I don’t know,” I said. “They went to a lot of trouble to hide their plan. That says complexity to me. But what do I know? This all happened years ago. Maybe we’re totally off track.”

“How about this,” Petra said. “When we get back to the office, I’ll start on a map. I’ll mark out the incident locations, the Cornerstone locations as we find them. Maybe if we start looking at it that way—not in sugar on a table—we’ll see some kind of pattern.”

“And we’re going to need to give the servers a very big tip,” Theo said, sweeping sweetener into a napkin.

“I’m suddenly craving a Chicago dog,” Petra said. “Anyone else interested?”

“Not me,” I said, and checked the time on my screen. “I have to get to Cadogan House.”

“Forgot,” Petra said. “You eat good over there?”

“Honestly, it’s probably pizza.” We were talking about my mother, after all.

THIRTEEN

I rode to Cadogan House in style—in the back of the Ombuds’ van, while Petra listened to a podcast about the extraterrestrial creatures living in our midst.

When she stopped to let me grab a bottle of wine for the party, she was talking about conspiracies. She was still talking about conspiracies when I got into the vehicle again. Petra was brilliant, creative, and skilled. And she’d never met a conspiracy theory she didn’t love. I still wasn’t sure if she believed any of it or just enjoyed the wackiness.