“I’m not sure which key,” Hill said as we reached her.

“Try the same one as before,” I said.

He did and the latch thunked. He pulled on the ring and the door swung open to reveal a large round chamber lit by the same flickering sconces that had illuminated our way since we’d stepped out of the elevator. A round, tapering structure squatted at the center, dominating the space.

Years ago I’d taken the girls on a tour of Hoover Dam that included the generator room where we’d stared in wonder at the huge turbines. This resembled one of those, only smaller. Its design had an Art Deco feel and looked…ceramic.

“This is it,” Ellie said in a flat tone. “The Prime Frequency generator.”

I stared at the thing and hated it.

I said, “This is what made you sick and burned you and put you in a coma? This is what changed you?”

She nodded. “As I said, wrong place, wrong time.”

I looked up toward an arched ceiling. “Then that means we’re directly under the center of the Sheep Meadow.”

“Not necessarily,” Ellie said. “Like my hidey hole, this chamber bends the rules of physics and geometry. It occupies its own space, one that’s not always where it seems to be. When it emits its signal, it’s under the Sheep Meadow. At other times, like now, it’s…elsewhere.”

Hill said, “I’m having a problem getting my head around that.” He looked at Hari. “You?”

“Yesterday morning I’d have been right beside you on the confusion boat. But after where I spent last night, no, it’s fine. Nooooo problem.”

Which seemed an odd thing to say. But I couldn’t let it distract me. I needed to know more about this thing.

“Who built it?” I said.

Hill shrugged. “Burbank told me the signals started in 1941, but according to his notes, the stairway and probably the tunnel were here when the Allard’s foundation was dug.”

I couldn’t stay in the same space as this thing. I walked back out into the passage and burst into tears. I wanted—needed—someone to blame. This big, gleaming, soulless inanimate object wasn’t filling the bill. I kicked one of the fist-sized stones littering the floor and sent it flying, wincing at the pain in my foot. I kicked another. More pain. I deserved it for letting Ellie lead us to the Sheep Meadow instead of insisting we go to the zoo as planned.

I’d let her go to where this contraption was lurking in the depths of the schist waiting for someone like her to come along.

Burning with sudden fury I picked up one of the rocks and charged back into the chamber. With a wordless cry of insensate rage I began hammering the side of the generator, screaming at it.

Hands pulled me away and pried the rock from my fingers as sympathetic voices tried to soothe me—the voices of Hari and Hill. Ellie stood silently by, watching with the eyes of a stranger, as impassive as the generator itself, which I hadn’t even scratched.