I came to this book with a certain amount of expectation, having seen glowing reviews in The Tablet and elsewhere. It didn't live up to my hopes, and it isn't anywhere near as good as Allen's other books.
Allen starts with an outline of how Opus Dei is structured, moves on to describe the founder's life, and then looks at how Opus Dei functions in the lives of its members. As the story progresses he looks at the various criticisms that have been made of Opus Dei. In the main he finds these unfounded and unfair, and he is clearly impressed with the particular model for lay spirituality that Opus Dei provides, most notably in the sanctification of work. The account comes across as bland, and, after a while, even as boring. It becomes difficult to see what the fuss is about.
Now it may be that that is the reality and there's no more to be said: that Opus Dei has a valuable spirituality to offer and that the criticisms of it are mostly unfair. If that had emerged as the conclusion, after a thorough analysis of the organisation and how it operates then one might well be convinced. Yet the analysis never goes particularly deep, and Allen's conclusions are flagged up from the outset; this leads to one not trusting how far he has really examined the issues. Compared with Allen's other books where he has combined even-handedness with insight and questioning, this one in the end disappoints.
One will find plenty of facts about Opus Dei, and probably come away better informed, so to that extent the book is useful. But as to just why so many people have been and are suspicious of Opus Dei, then the book left me at least still wondering.