A former believer but now an agnostic, he is also an expert on the historical use of symbols in Christianity; that special knowledge is the key to each of the stories. Each of the novels in this series revolves around a centuries-old struggle between believers and a shadowy organization known simply as The Garden, which has devoted itself, working entirely in secret, to the destruction of the faith. Manipulating events from behind the scenes, the Garden has devoted itself patiently over the centuries to what it calls 'snakebites'---causing tiny scandals here and there, enough to shake people's faith just a little, hoping, as time passes, that the cumulative effect of its work will bring an end to belief."