In the book there are two interwoven narratives, one concerning a Roman family struggling to survive, the other concerning a modern day hero trying to solve the mystery of his family. Unsurprisingly they are connected, and initially this feels like a Dan Brown historical mystery thriller (or thrilling mysterious history?). However the mystery Baxter is building towards has nothing to do with the origins of Christianity, even though his mysterious organization passes itself off as a Roman Catholic - this is a more sinister, more biological and more sci-fi concept.
What is it that's so good about this book? The mystery is revealed gradually, this is handled well without seeming to hold back facts unfairly (I am often irritated when I read that the protagonist of a story has just learned a key fact but I am not informed until two chapters later); The case for plausibility - basically that similar phenomena do exist in several places in the animal kingdom - is worked in neatly; the complex concept at the heart of the novel is described clearly; and the ending turns the story on it's head - instead of describing a freak occurrence as I thought, are the principles of this book central to understanding all human activity?
It hardly seems fair to identify any faults at all with such a powerful book but it's difficult to imagine all the evolutionary changes described in humans occurring over "just" two thousand years. The quality of the writing helps to minimise this; also some suggestions (that the process could actually have evolved earlier in human history, and remained within the human genome as a vestigial capacity or a dormant process re-activated by stress) are hinted at later in the series.
The ending, together with extracts from the sequel printed at the end of the book, give the impression that this theme will be developed further in the sequels - particularly Baxter's future history of child warfare seems initially to be built on the same principles; sadly, while the Coalescence does rear it's head again this concept is underdeveloped.