In a lab under the last city, a young technician puts a fragment of the enemy under a microscope and finds something nobody wanted to find: a maker's mark.
The old manager of the wreckage floor knows it on sight, and tells the story his whole building was built on top of — an empire, a divide, a man named Toni Clattus who gave the working class one voice, and the genius who was ordered to silence it. The first machine ever given intelligence. A core the size of a fist that could light a city. A name: Marcus. Exiled a century ago to a prison station called Tartarus, dead by every reasonable measure — and signing new work.
Meanwhile, Mary is marched past Hannah's room and finds it empty. The power that abandoned her in the street comes back before she finishes asking the question — because this time it isn't for her — and the last city learns what its corridors are worth against the whole descent of the sea. The answer arrives on silver wires.
Some cages are built of steel. The better ones are built of people you trust, saying please.