The sequel to The High House. Spoilers ahead for that.
Shortly after the events of that work, Carter is once again in Innman Tor, where the anarchists are still going after whatever they were after when they destroyed the Tor. Then he formally visits Count Aegis, who's now in charge there.
The count's older daughter Sarah tries to collect herself, certain he will be all disapproving of how her father is running it. Her younger sister Lizbeth -- adopted by the count after her anarchist father vanished in the last book's trouble -- is more excited. And the meeting goes rather better than Sarah expected. Lizbeth gets along well with Duskin, and then Carter returns, often, and Lizbeth gets to flit about him and Sarah until finally they are having the dinner to celebrate, and Lizbeth is kidnapped by her father.
The anarchists haul her away to a mysterious house without windows. She can grow only brambles in the garden. And for years, they keep her there. She tries to send messages in a bottle down a stream.
Six years later, Carter and Sarah have had no children and still wonder what happened to Lizbeth. But then things start to happen. Enoch sees things that changed when he went to light lamps, and they notice it is far more regular than it had been. Duskin, returning from hunting gnawlings with his friend and cousin Gregory, goes with Carter, two architects, and a small group of guards to investigate.
It involves a man who had fought for the anarchists, several secret anarchists, Lizbeth thinking that Duskin is Carter, Jorgamund suffering horribly from a fierce winter storm, an aviary where all the birds have been turned to something mechanically orderly, and much more.