“What is it?” I round the desk. Kai’s bent over a square cut into the floor, the hinged wooden panel resting open beside her.

“A hidden passage.” She turns on her flashlight and shines it into the hole. “This must connect to Gaia’s suite.”

“Why would you think that?”

She stills, her mouth opening and closing again as she shrugs. “Just . . . you know . . . rumors. After Gaia and Lyon fled the Observatory during the rebellion, people talked. If they really were secretly in love, plotting to be together for years, they must have had a way to be together without Michael knowing, right? I bet this was it.” She turns back to the passage too quickly, as if she’s uncomfortable meeting my eyes. She leans down into the hole, one hand braced on the lip, the other holding her light. Her hand slips off the edge, and I grab the back of her jeans before she goes tumbling through the opening. Papers crunch under my fist as I haul her upright.

“What’s this?” I ask, catching the thick stack of folded sheets as they slip from her back pocket.

“Nothing.” She reaches around me, desperate to get it back. But she’s too short and my arms are too long, and in a second, I have the folded papers peeled open. At first, I can’t make sense of the sketch—a cross cuts through the middle of the page, each cardinal point snaking off the edge of the paper. The perfectly straight lines bisect a labyrinth of softer curving, forking ones. Tunnels. Dozens of them. Swirled with narrow sets of hidden circular stairs, all labeled in Lyon’s handwriting.

“This is a map of the catacombs.” My eyes dart over Lyon’s neatly printed markings. The paper is thin, the ink faded with age and the creases worn. “Where did you get this?”

“It’s mine,” she says, still reaching for it. “Lyon gave it to me.”

“When?”

“A long time ago. Give it back!”

I hold it higher, out of her reach, the light from the hallway shining through the paper, revealing other faint markings. A second piece of paper clings to its folds, and I peel the pages apart. This second map is familiar, full of landmarks I recognize. The Crux at its center, the Control Room below the east wing. The Hall of Records below the west. And to the north and northeast, two expansive apartments, one labeled “Chronos’s Suite” and the other “Gaia’s.”

A thin dotted line connects Gaia’s apartment to a space below the Winter wing, close to where we’re standing. I hold the two maps together against the light, overlapping their creases until they’re perfectly aligned. Four lines disappear off each end of the page, one in each wing, marked “emergency escape routes.”