The Intelligencer by Leslie Silbert
A man and a woman team up to decipher an old manuscript that contains secrets that someone is willing to kill for. The Da Vinci Code you guess? No, but its just as exciting and intriguing. The manuscript is a 16th century journal of a spy master laying out the intrigues and hidden scandals of Elizabethan England. Mix in sinister art collecting millionaires, Iranian defectors, torture and murder and you have a whopper of an adventure.