An American mathematician's assignment in Russia spirals into a high-stakes maze of shifting loyalties and intrigue in a propulsive short thriller by #1 New York Times bestselling author Lee Child. Nathan Tyler is an unassuming professor at a middling American university with a rather obscure specialty in mathematics-in short, a nobody from nowhere. So why is the White House calling? Summoned to Washington, DC, for a top-secret briefing, Nathan discovers that he's the key to a massive foreign intelligence breakthrough. Reading between the lines of a cryptic series of equations, he could open a door straight into the heart of the Kremlin and change the global balance of power forever. All he has to do is get to a meeting with the renowned Russian mathematician who created it. But when Nathan crashes headlong into a dangerous new game, the odds against him suddenly look a lot steeper.