Harry Turtledove has carved out a substantial niche in the alternative history genre, with multiple series of novels exploring what the world would be like after the South won the US Civil War, post an American Revolution that failed, or in which the German Reich was victorious in WWII, among others. In the Presence of Mine Enemies is a stand-alone novel in that "Germany Won WWII" universe, but it does not require any further knowledge of Turtledove's alternate history than that statement.
This is a fairly dark tale of Jewish families living in disguise in 21st-century Nazi Berlin. Heinrich Gimpel eats pork, swears "Jesus!" and "Christ!", crosses his heart to betoken a truth-telling—and celebrates Passover and Chanukah quietly at home with his family and other Jews who do the same. The German Reich is confident that Jews have been exterminated; yet they still teach their children a casual, attenuated hatred of the kind we reserve for the wicked witch and the troll under the bridge.
The story centers on Heinrich, his Jewish friend Walter who has hacker-level access to the SS genealogy databases, Heinrich's daughter Alicia who at age 10 has just learned her family's secret, and Frau Professor Doktor Susanna Weiss whose gender seems to be more of a hindrance in her life than her secret background. Each of these central characters faces a personal choice to continue as a Jew and retain the secrets of all in their group.
Turtledove's expertise in building alternate histories illuminated by the knowledge of real history shows in both subtle and blatant ways: a Yeltsin-like mounting of a panzer tank that sidelines the Gorbachev-like Führer, a Chernobyl- or Bopal-like disaster that kills "an unknown number of Untermenschen", and of course, Führer Kurt "Haldweim".
The novel was expanded from a short story by the same name, and retains only a trace of its small-format origin (chiefly in too-frequent repetition of "what if we got caught, oh no!" musings by the principals.)
At a time when it is common to accuse one's political opponents of "Fascism" and draw parallels between Hitler and whoever, it is valuable in itself to be reminded what those terms actually meant and what it might feel like to live under such a regime. If for no other reason, I can strongly recommend this novel.
David Roy of Curled Up With a Good Book finds Turtledove's writing wooden and "pleasant" but "no Merlot".