This well-researched and captivating study analyses the involvement of German princely houses in the Third Reich, focusing on the activities of princes Philipp and Christoph von Hessen-Kassel as a lens through which the German higher aristocracy's orientation towards Nazism is examined. The highly visible and prominent Hessen-Kassel family was related to the Hohenzollern and British royal houses, since Phillip and Christoph's mother, Princess Margaretha von Preussen, the child of Queen Victoria's eldest daughter Victoria and Emperor Frederick III, was the sister of William II and niece of the British King Edward VII. Petropoulos's detailed investigations, including the holdings of well over a dozen archives, were supported not only by members of the Hessen family, who put the family archives and important documents at his disposal, but also by Prince Philip, Duke of Edinburgh, who shared his personal recollections with the author. Philipp (born 1896) joined the Nazi Party early, in October 1930, and eventually became the highest ranking state official (Oberpräsident) in his home province of Hessen-Nassau, as well as Hitler's personal emissary to Mussolini. Philipp lost two older brothers in World War I and participated in combat himself. In 1925, he married Mafalda, the second daughter of King Vittorio Emmanuele III of Italy, a happy marriage though not without complications. One big complication, according to the author, was Philipp's relationship with the British poet and writer, Siegfried Sassoon, in the early 1920s, which Petropoulos documents in detail. Sassoon, though clearly close to him, provides a scathing character assessment of Philipp, considering him ‘rigid … an example of conventional culture … impervious to any arguments … his culture consists in acquiring information without coordinating it … [and is of an] intellectual rigidity that will develop into ossification’ (p. 70). Sassoon, who also wondered whether he was ‘only one of P's regular succession of affairs’ (p. 71), was also offended by Philipp's ‘inability to distinguish between decent and indecent people’ (p. 71). This turns out to be plausible criticism in light of what was to come.