Gerard Russell: "Heirs to Forgotten Kingdoms: Journeys into the Disappearing Religions of the Middle East". Looks at first sight as if it's going to be a simple travelogue, but he builds up a surprising and systematic picture of hidden relationships between the belief systems of that part of the world for the last 3000 years or so, with groups that are now utterly marginal given far greater historical importance than you'd think. (One limitation is that he didn't know about the much older Göbekli Tepe site, which has to change the way we think about all these religions; but that's rather speculative as yet).

I would love to have seen an Essene community on the Sabbath. They had to go the whole day without taking a shit.