The Codex Cumanicus was a strange little book. A thirteenth-century lexicon of Latin, Persian, and Turkish attached to a collection of fourteenth-century riddles in Turkish and medieval German, it fascinated Dr. Marion Bailey. But now, in 1935, it was about to take on new meaning. Unknown to Marion, a previously unstudied copy of the Codex--naming and identifying British intelligence resources throughout Azerbaijan--has recently surfaced at the British Library, thwarting a British plan to recover Caspian petroleum lost to the Soviet Union a decade before. When Jeffrey Willcox, Marion's husband and political adversary, calls on her to explain how a six-hundred-year-old manuscript could expose an ongoing and secret government policy, she refuses. But after reading the manuscript, she comes to a startling conclusion. Neither the Codex nor British policy in the Caspian have ever been concerned with access to petroleum. On the contrary, their target is far worse. Terrified by her discovery, she races against Jeffrey and his office to try to neutralize the threat. Travelling from the ice-bound arctic circle to the seething mud volcanoes of Azerbaijan, Marion searches for a way to forestall the inevitable. What she unearths could alter the outcome of an emergent World War.