Re-read this earlier this year, and it remains fantastic. Powers is one of those incredibly under-appreciated writers in spite of all his awards, and his ability to use real-world history in his storylines is always fascinating (The Stress of Her Regard, in which Keats, Byron, and Shelley fight a lamia, is still my favorite).

This is a Cold War spy novel with supernatural fantasy added, focusing on Kim Philby and the atrocities of Stalinist Russia through the lens of a British spy named Andrew Hale. It's essentially Le Carre with fantasy added.

But what really makes it work is that Powers made a rule for himself to not let anything in the book depart from known history. So Philby, TE Lawrence, and any other historical figures (or events, like an earthquake) have to be when and where they were known to be. And in turn, that makes the eventual reveal of what's going on at Mount Ararat even more horrifying than if this had been a typical "big monster rampaging" kind of book.

It does have some non-linear storytelling (jumping around a couple of different time periods), and throws in everything from the Dead Sea Scrolls, to The Thousand and One Nights to Noah's Ark (I mean, Mount Ararat is a big clue there).

I want to avoid spoilers (even though it's twenty years old), but if you enjoy Cold War spy novels, especially ones where the USSR is really, really bad, and if you also like fantasy elements, this is well worth the read.