It's June the fourth, 1944. D-day minus two. A sleepy Sunday morning in Leatherhead, sorry. Two men in suits approach the home of local headmaster Leonard Daur, but they're not here to ask him about the day job. For almost two decades, Daur's had a side gig as one of the Daily Telegraph's top cryptic crossword setters. But the men on the doorstep believe this mild-mannered teacher may hold his own secret meaning. They're agents of the Security Services, MI5, and they're concerned that Leonard Daur is a German spy. Daur's crossword puzzles are typically esoteric, but over the past month, they've included a number of suspicious clues. One of the US, the answer, Utah. Red Indian on the Missouri, Omaha, and most recently, Britannia and he hold on to the same thing. The answer to that one is Neptune, the code name for the vast naval operation due to take place in less than 48 hours. Other solutions include Juneau, sword, and gold, even the more obscure Overlord and Mulbury. Dauze's back catalog Daur holds a few surprises as well. Two years earlier, one of his puzzles included the solution Dieppe, just two days before the disastrous raid on that particular French port.

It's not looking good for the headmaster minister. The spooks, as he later puts it, turn him inside out, doing their best to extract a confession. The questioning goes on for hours. Where did Daur get the D-day code names? Is his brother-in-law at the admulter involved as well? Who is deciphering his messages in Germany? What other top secret material is he leaking? But despite their best efforts, the MI5 agents are getting nowhere, and the clock is ticking. The D-day armada will soon begin massing in the channel. However hard they push him, Leonard Daur refuses to budge. He's just an innocent teacher, he tells them, one who enjoys a bit of mental gymnastics on the side. Daur insists he knows no more about the invasion plans than your average man on the street. And if he did, he certainly wouldn't be putting it in his crosswords. The thing is, by the time they've finished with Daur, the two agents are inclined to believe him. And they're right. The headmaster is no spy, but he has been publishing top secret information. Struggling to juggle the crossword setting with his busy teaching schedule, Daur has been leaning on his pupils for help, handing out blank grids for them to fill with words, and then writing clues to fit their solutions.

A 14-year-old boy called Ronald French, it turns out, is the real source of the D-day leaks, though Ronald is as shocked as his headmaster when he finds out the trouble he's caused. Hauled into Daur's office. He confesses he overheard the code words from the American and Canadian soldiers billeted nearby. All the boys know them, he tells the horrified headmaster. Ronald produces a notebook containing all the top secret terms he scribbled down. Mr. Daur orders him to burn it immediately. The D-day crosswords are a puzzle that could have cost the Allies dearly. Because in the weeks leading up to the invasion, British agents are working flat out to fool the Germans about the specifics of Operation Overlord. Everyone knows the Second Front is coming, but when and where? Those are the most closely guarded secrets in the world. In fact, unprecedented resources have been committed to deceiving the enemy about the Allies' actual battle plans. The British are setting a puzzle of their own, and this one involves fake officers, fake spies, even an entire fake army. From the Noiser Network, D-Day The Tide Turns, available from June sixth..