“To the Vault of Ages,” Isabelle said. “That world we were just in. That’s the one Hasdrubal wants. The dead world. The broken world. The end of everything.”

Bitterlich scooped Rebecca up lightly, cradling her head. “I’m coming.”

“I don’t think you can,” she said. “The Vault of Ages isn’t a place you can reach from here, not without the reliquary.” She gestured at the towers around them. “When the world ended, four things remained: us, these ruins, the stars, and the Vault. They are constants. They are part of the original design. Everything else, our world, our sorcery, it’s just … painted on somehow, and the Vault is painted out.”

She approached one of the broken towers. They were wide cylinders packed closely together and then chopped off a few stories aboveground like rushes in a swamp. In the darkness the metal throbbed with a light that did not spill beyond the surfaces, and behind those pulses spun the shadows of gears, axles, catchments, and rockers that ticked and tocked in directions beyond the three the human mind could easily comprehend. What did you do if you didn’t have enough space in your gearbox? If you were the Builder in his workshop, you just added another direction and multiplied your space, so that your gears might mesh in one place and their axles might intersect without interacting. Isabelle could see how the foundations of the math might be laid, if only the stubbornness of space could be overcome.

She touched the metal with her spark-arm and dove in. Inside the metal a whole new city spread out before her. It was a city of silver pathways that sang like harp strings and clockwork junctions that whirled driven by the Builder’s limitless engine. Much of the city was broken and smashed, its chords dissonant and its pathways dark, but all of it was there. All except a hole where nothing was, a tight spiral that warped the space around and inward and then disappeared into its own center like a snake eating its tail.

Isabelle reached for the center of the spiral and found it clenched tight, held shut by something on the other side.

Found you.

Isabelle returned to her body and shook herself. Her feathers shivered. Rebecca was back on her feet but woozy.

Bitterlich asked, “What happened?”

“I found the door.” Isabelle led them both up a few streets toward the center of the ruin. The road curled around a circular tower and just kept curling beyond the place where the circle should have completed. Two other roads met here at a point, like the center of a triskelion.

“It’s here,” she said, wafting her hand through the point in space where the door must be. Hasdrubal brought the reliquary here and it opened for him.

“Can you open it for us?” Bitterlich asked.

“I’ll be lucky if I can squeeze myself through it,” she said.