Zoe Wilder has the unflashy, solitary life of an academic, studying ciphers in literature at a California university. When her research takes her to a cryptology conference in Madrid, she's not expecting to kick off the Enigma Challenge, a clandestine puzzle competition few dare to enter. The Enigma Challenge is an infamous competition with impossibly high stakes: Lose, and your identity is wiped forever. It doesn't take long for Zoe to realize that she's in over her head. Enter Dane Seaver: the mysterious hacker who insists they team up. Dane knows the Enigma Challenge - its secrets, its players - and Zoe knows ciphers. For better or worse, they need each other. Six days, five puzzles, three countries, and innumerable rivals. What s more, the spark of attraction between them becomes harder to ignore, but distractions are dangerous. With twelve million dollars and multiple lives on the line, the Enigma Challenge is anyone s game. Will Zoe and Dane come out unscathed against the other players - and each other?