The record of Pope Pius xii during the Second World War continues to provoke fierce debate – and a great many different kinds of treatment. Some are sober; most are polemical, even disputatious. Much of this work has occurred in the United States. The author of this new book, Mark Riebling, is here described as ‘a path-breaking writer on secret intelligence’ who has previously published a study of the two great American investigative and intelligence agencies, the CIA and the FBI. Does this augur well, and does such a book add anything to an area of research which has attracted the attention of many committed scholars? It would be inadequate to commend or deprecate Church of spies as an exceptionally well-told story which thrives on a vivid sense of detail, a lively appreciation of character and a superb sense of drama. The book certainly possesses all of these qualities. But Riebling has worked his way through the intricacies of many archives (a list of them runs to almost five pages) and much of the authority of his work is based on solid claims. His cast of characters is formidable and his essential task is to capture their interweaving narratives with clarity and to show them at work. The extraordinary figure of the German lawyer Josef Müller strides heroically across these pages, rubbing shoulders with, and carrying messages for, a considerable host, clerical and lay, most of them German: Ludwig Kaas, Robert Leiber, Wilhelm Canaris, Konrad von Preysing, Claus von Stauffenberg and Helmuth James von Moltke. What, then, of the figure of Pius xii? However carefully concealed, there can be little doubting where Riebling's own sympathies lay. He adroitly establishes at the outset that his book does not seek to answer the many who have since accused the pope of failing the persecuted Jews of occupied Europe. He has a different, though related, task. If his treatment is dramatic, it is also free from occluding polemical priorities. The narrative presents a pope caught up in the tragic turmoil of the age, anxious, watching, listening, manoeuvring, endorsing and even licensing – a participant, not an abstainer. Not quite a spy-master, but with a natural, and purposefully cultivated, penchant for secret affairs, Pius xii played, as best he could, a prayerful, ‘defensive game’, in which fundamental affinities – found in a number of long-term alliances and brief connections – were expressive in a greater theatre of active resistance against Hitler. Indeed, at certain junctures the Vatican could even provide the vital dimension. In short, the widespread idea that Pius xii was ‘Hitler's Pope’ has much to face up to in a book like this. Mark Riebling has made a serious contribution to a debate that has become both scholarly and popular and he has judged both his material and his audience with great confidence.