This unconventional, ultimately charming book tells the life story of the Mexican lay Catholic activist Sofía del Valle, a striking figure in the transnational Catholic milieu of the 1920s and 1930s Mexico and the US. The thesis is Sofía's life itself, explored chronologically as an example of the possibilities and limitations of Catholic women's activism, a particularly significant force in twentieth-century Mexican history. At the same time, readers should be advised that the book is experimental in form, an attempt to bring Sofía back to life simultaneously as historical agent and historical memory. Thus it is divided into no fewer than thirty-four short chapters, most only a few pages long, detailing aspects of Sofía's life; these sections are interspersed with ‘interludes’ consisting of the author's subsequent encounters with Sofía's descendants, who remember her in often candid fashion in various Mexico City houses and cafés. There are also lots of pictures of Sofía inserted into the text. In this way, The mysterious Sofía functions as a kind of double biography, being the story of Sofía's actual and posthumous lives. The effect is a bit like leafing through a family album detailing Sofía's life or, perhaps, a 1920s fotograbado magazine, while listening at the same time to a family group talking about the person in the photos.

Some readers may find this off-putting, unnecessary or, worse in a biography, obfuscating; personally, I did not, although an additional conceit (the middle section likening Sofía's journey as political Catholic to a ‘Mexican odyssey,’ replete with classical quotations) did seem a bit much. Still, formal experimentation is rare enough in the Mexicanist historiography, and perhaps should be applauded when done well (the closest comparison, perhaps, being Jean Meyer's Yo, el francés, which interjects the author's family story into a compilation of letters written by French soldiers during the Napoleonic invasion). More importantly, Sofía's life is robust and stirring enough, and the underlying research scholarly enough, that those who stick with The mysterious Sofía will be rewarded with a singular appreciation of Catholic women's action in Mexico. By the end, readers will care about Sofía and at least admire her pluck. They will have far more knowledge of her Catholic world and of how women could and did operate in it. Indeed, the picture of the Church that emerges is not just transnational but almost semi-matriarchal, an institution responding not to clerical imperatives alone but the efforts of talented women such as Sofía, who was semi-integrated into the Church's power structure via a life-long platonic coupling with Bishop Miguel Darío Miranda.

Sofía herself – chic and Gatsbyesque on one hand, celibate, spiritual, physically troubled and politically militant on the other – was certainly a persuasive, memorable character. Thus we see how she helped to consolidate the Mexican Church after the 1929 peace deal signed by the Mexican hierarchy and the post-revolutionary regime. We also see how she educated young women within the confines of Mexican Catholic Action (ACM), having previously supported the Mexican Social Secretariat (SSM) and moralised Ericsson telephonists (one of the less creditable instances of her life, since Ericsson's labour regime was oppressive to the point that celibacy pledges were required of women employees). For good measure, Sofía later ran a shoestring Catholic girls’ school in Mexico City during the cristero war (1926–9). Later, from 1934 to 1938, Sofía toured the US raising funds and consciousness on behalf of Mexican Catholics. At this point, Sofía earned de facto recognition from the US episcopate as the Mexican Church's official representative and was interviewed by Catholic shock-jock Fr Coughlin. Another measure of her international prominence was that the Mexican government now tried hard to discredit her, splashing intercepted correspondence to Mexico's bishops on the front pages (1934), where Sofía was portrayed as a Catholic Mata Hari plotting seductively against her country (hence the ‘mysterious Sofía’ of the title). These are perhaps the key sections of the book in which we see Sofía flourish in a transnational medium, not just because Church politics required it but because she was a plausible example of a kind of Catholic modernism. Yet it was a constant personal struggle, not homeric destiny; Sofía's personal Catholicism was steeped in the ‘little flower’ spirituality of humdrum sacrifice made famous by the French religious Thérèse de Lisieux, and in one scene we find her overcome with pious emotion on visiting Thérèse's shrine. Sofía seemingly felt as if she had to fill the modern clothes and shoes that she wore. Another scene finds her ironing a skirt that was soaked in a thunderstorm minutes before meeting a bishop, only to find that the garment had shrunk, raising its hemline above the knee. The book as a whole is filled with suggestive vignettes of ambivalent Catholic modernity.

Andes follows Sofía's life vicariously to the end, through the story of her advancing dementia and closing with a moving visit to the crypt in Mexico City's Metropolitan Cathedral. Here we learn that, in death, a woman who had worked indissociably with Mexican and US Catholic hierarchs for decades and maintained a close but appropriate relationship with a man as powerful as Mexico's first cardinal (Miranda) was symbolically detached from those who in life had treated her as their virtual equal, their feminine alter ego, and had done so with good reason. In the conclusion, the author walks the seventy-seven steps separating Sofía's subterranean resting place from Miranda's (p. 357): it feels like an uncomfortable, echoey and entirely inappropriate distance.