Hector Longstreet should have retired years ago, but he still teaches Latin and Greek at a school in England because it's the middle of the Second World War, and the younger schoolmasters are serving in the military. However, Hector's real interest in life is composing cryptic crosswords. His puzzles, published in a British Sunday newspaper, end up in the hands of the Germans. Is he passing secrets to the enemy via the answers to his fiendishly difficult clues, or perhaps via the clues themselves? Or is the crossword traitor Bridget Hawkesbury, another composer of cryptic puzzles, who was trapped in Germany when war broke out? Bridget is imprisoned in an internment camp in Upper Silesia. The camp commandant gives her Hector's puzzles to solve, after which he forwards her solutions to German Military Intelligence in Berlin. And what about the crossword set by MI5 officers to inform the Germans where the D-Day landings will take place? This fast-paced thriller has clues aplenty-but few answers until the exciting finish.