“What does Grant Park have to do with ley lines?” Theo asked.

She gave him a flat stare. “Are you serious?”

“Yes?” he asked, his voice now uncertain.

Petra rolled her eyes. “I guess I’ll need to lay it out for you.”

“Please do,” Yuen said, amusement in his dark eyes. “And nice pun.”

“Yes, it was.” She used her smaller screen to direct the large one, flipping through faded drawings to find a scratchy sketch of what I thought was Lake Michigan.

“The North American Journals of Prince Maximillian,” she said. “He traveled the US in the 1830s, did these amazing natural-history journals where he recorded plants, animals, food, people, landscapes. Not much of Chicago at that point. But he didn’t need the buildings to see this.”

She zoomed in to reveal three lines that ran across the edge of the lake near where I guessed Chicago sat today. One crossed the city from east to west. The others were angled, one running southwest to northeast, nearly vertically, through the middle of the city, the other running northwest to southeast at a shallower angle.

“Two of the lines cross near downtown Chicago,” Petra said, pointing at the map. “But the actual ley lines are only a couple of feet wide, so the scale is totally wrong on this map.”

She swiped a screen and pulled up more data, and the overhead monitor showed a satellite image of Chicago marked by three glowing, intersecting lines.

“These are Chicago’s ley lines,” Petra said, beaming like a student who’d just nailed a recital. “I used satellite images, surface temps, wind data, and jet-stream movement, along with a sprinkle of human activity, and these are the lines predicted by that formula.”

“They’re real,” Theo said, looking back at her with awe. “And you actually found them.”

“It’s more accurate to say I found the echo of them, the place they’re algorithmically predicted to be. We don’t have the knowledge to detect them per se, so this is the next best option.”

She zoomed in, and the lines grew clearer, crisper, thinner, until they crossed just off Michigan Avenue, just south of the river.

And right over Grant Park.

“There’s a ley line conjunction beneath Grant Park,” Theo said, gaze intent on the screen.

“There is,” Petra said, then looked at us. “Have you figured it out yet?”

We looked at her, then the map, trying to figure out where she was leading us.

“No?” Theo said.

With a heavy sigh, Petra pulled up another photo. This one was an overhead shot of the fairies at Grant Park, the careful lines in a V configuration, with Theo and me tiny dots in front of them.

The fairies’ formation matched the ley lines perfectly.

“That’s why they were in that V configuration,” she said. “They were standing over one of the angles created by the conjunction.”

“Damn good work,” Yuen said, and his smile was as wide as Petra’s had been. He seemed genuinely proud of her work, which I suspected wouldn’t have been Dearborn’s reaction.

“Thank you,” she said.

“So the fairies wanted to use the ley lines for something,” I asked. “And they figured the conjunction—two ley lines crossing—would give them the biggest bang for the buck.”

“Maybe,” Petra said. “We don’t know much about the mechanism of ley lines because of—”

“Big Petroleum,” we finished for her.

“Hilarious,” she said without a hint of humor. “And correct. But presumably they want the power.”

“Ruadan wants the power,” I murmured, stepping closer to the map and wondering what he had planned.

“If they wanted the conjunction,” Theo said, “they might try Grant Park again. Or the next best thing, which I guess would be anywhere else along the ley lines?”

I nodded. “So if we search the ley lines, we might find the fairies.” And then the obvious thing hit me. “Can you put the Potter Park tower and the castle on that map?”

Petra looked at me, grinned. “Of course,” she said with a nod. “Of course they did that.”

She knew what I was looking for. And when she plotted the two structures on the map, she showed my instinct had been right.

“They’re positioned over ley lines,” Theo said.

“Claudia probably selected the Potter Park tower because of the location over the north-south line,” I said, “and bought the castle property for the same reason.”

“We’ll get CPD officers to travel the lines, look for any sign of them. Can you get me a scalable version of the map and the course of the ley lines to pass along? Perhaps one that, just in case of Big Petroleum, doesn’t actually say ‘ley lines’?”

“Sure,” she said. “No one has to know what the lines represent. We can call them . . . fairy migratory routes or something.”

“That’s good,” I said.

She smiled, which crinkled her nose. “Yeah, I like it, too.”

Yuen’s screen buzzed, and he pulled it out. “I think our luck is changing,” he said, and swept a finger across the screen to send an image to the larger monitor.

The image was dark, but it showed side-by-side images of a fairy. In the first, the neck of his tunic was pinned with a gold pin. In the second, the pin was gone.

“Cadogan House surveillance video,” Yuen said. “These images are from the evening of the party. And, interestingly, they are the only images of him at the event. There are none of him entering through the front gate or speaking to the other guests.”

“Like he was there for a very short time,” Theo said, “and a very specific purpose.”

“Precisely,” Yuen said.

I closed my eyes and walked through the scene, trying to put myself in the fairy’s place. “He wants to stay undetected, so he avoids the front gate. Instead, he comes in over the wall. He kills Tomas, magicks Riley and gives him the knife, then sneaks out over the wall again, leaving his pin behind, then disposes of his bloody clothes.”

“And the only evidence we have of any of that is circumstantial,” Yuen said.

I nodded, opened my eyes again. We were getting closer. But we weren’t there yet.

“We’ll put out an APB,” Yuen said. “But I suspect we won’t find him until we find the rest of them.”

“You’ll let me know if you find him?” I asked. “And the SUV?” At worst, Claudia was in danger. At best, getting her back might help stop whatever the fairies were trying to do.”

“We will,” Yuen said. “While I’m still not entirely convinced by your Rogue-vampire argument, it would be wrong of me to discount your contributions. So thank you.”

“You’re welcome.”

“If we don’t find anything before dawn,” Theo said, “we should get together at dusk. Give everyone an update.”

“Arrange it,” Yuen said, then glanced at me. “And in the meantime, if you could stay out of Dearborn’s line of sight, all the better.”

* * *

• • •

I left the Ombuds to their work and took an Auto back to Lulu’s place, where I’d had my mother messenger the suitcase I’d left at the House.

She’d seen the news about Grant Park and had waited up for me. Even Eleanor of Aquitaine seemed a little mellower—hissing at me only once as I walked past her.

We turned on some Blondie, sat down in the rainbow of light that reflected off the windows, and worked on a box of crappy wine.

She sipped her mug of rosé. “Times like this make me wish I’d chosen the magic route,” she said, ankles crossed on the coffee table. “That I could snap my fingers, and everyone would act the way I wanted them to. No one would get hurt.”

The rosé was terrible. So I drank some more. “I don’t think magic works that way.”

“Do you know why I say no to magic?”

“Because of your mom?”

“That’s part of it. Because magic—the entire world of supernatural drama—makes me feel powerless. It makes me feel like that little kid who was mortified by her evil-villain mother, who didn’t have a choice.”

“Your mother is a good person.”

“With an addiction, and who hurt a lot of people because of it.”

“No denying it,” I said. “I think it’s all about choice. About decisions. For a really long time, I felt like I didn’t have any. So I decided to make some, starting with going to Paris. And, I guess, staying here while the rest of them ran back. Those are just choices. You make the choice, and you take the next step.”