After 10 years' service as a cryptographer with MI6 during the cold war, the extremely shy and reclusive George Withers becomes editor and compiler of the Sunday Times crossword. 30 years later and now in his 60's, an old MI6 colleague asks him to place a code within the Sunday Times cryptic crossword puzzle. George is totally unaware the code is a catalyst for a number of gruesome deaths around the world. The Serbian father of one of the victims discovers the puzzle maker had something to do with his son's death, and goes on the hunt. Georges' quiet world of puzzles changes into a nightmare hunt through the streets of London. While on the run he tries to decipher that last fatal cryptic code in the puzzle he got from his friend, who has now disappeared, and hopefully save his own life and others near to him.