In 1941, a small subgroup of the English government negotiated peace with Hitler. Now it's the 1960s. Japan has dropped atomic bombs on the Soviet Union, the US is isolationalist and utterly unconnected to world affairs, and the UK has been shipping undesirables overseas to German concentration camps for nearly two decades. It's a fascinating alternate history, and one that is made particularly chilling by how solidly Walton crafts it.
Carmichal was a mere Inspector from Scotland Yard in the first book of this trilogy, but he has progressed to head of the Watch (the British secret police, focused particularly on Jews and political dissidents). A thoughtful man of principles and deep loyalties, he has nevertheless made a series of compromises and betrayals over the years. While outwardly he is the most threatening man in Britain, in private he is focused on three things: keeping his lover, Jack, safe; creating a genteel life for his ward, Elivra Royston; and smuggling Jews out of the country to safety. But he cannot juggle all three at once forever. When Elivra is accidentally embroiled in a plot to depose the Prime Minister, she and Carmichal will be forced to sacrifice much that they held dear.
In each book of the Small Change series, the tone has darkened; by this, the final book in the trilogy, matters are grim enough that greeting someone with "So I hear you're a fascist" is not an insult, but a complimentary bit of small talk. An entire generation has been raised with horrific values: even Elvira, a kind girl with intentions toward Oxford, thinks nothing of throwing rotten fruit at Jews. Walton does such an excellent job of slowly but surely tightening the noose that when relief does come, it feels a bit unearned. As much as I wanted to, I simply could not believe the ending of this trilogy. This is a series that deserves four stars at least, for its impeccable, thoughtful worlbuilding, nuanced character portraits, and chilling plots. But I can't help but feel a bit let down by the end.