For nearly 300 years, the mysterious journal of Jacobite exile Mary Dundas has lain unread -- its secrets safe from prying eyes. Now, amateur codebreaker Sara Thomas has been hired by a once-famous historian to crack the journal's cipher. But when she arrives in Paris, Sara finds herself besieged by complications from all sides: the journal's reclusive owner, her charming Parisian neighbor, and Mary, whose journal doesn't hold the secrets Sara expects....