Zara Dunne, an ordinary office worker at the London pension fund firm Lochmill Capital, finds her life upended when a group of high-tech armed robbers storms her office. Forced to help execute a massive £4 billion heist, Zara is thrust into a dangerous world of financial subterfuge, MI5 conspiracies, and shifting alliances. As a relentless detective with his own gambling demons investigates, Zara must navigate a web of secrets to protect herself and uncover the true mastermind behind the "heist of the century".