The Queen of Crime, Agatha Christie, was so carried away by the plot of one of her thrillers, MI5 feared she accidentally gave away one of Britain’s biggest wartime secrets.

According to the Telegraph, Christie was a close friend of Alfred Dilwyn “Dilly” Knox, a leading British code breaker, so MI5 was concerned when a character called ‘Major Bletchley’ appeared in her 1941 novel N or M?. 

The novel revolved around a detective duo Tommy and Tuppence, a married couple who tracked down German spies in Britain. In the novel they also encounter an old Indian Army major, Major Bletchley. MI5 feared that the character was based on the Bletchley codereakers’ knowledge of German plans during WW2.

The team at Bletchley Park managed to break the German Enigma cipher machines, enabling British intelligence to intercept German messages. 
While the Germans thought their Enigma code was unbreakable, it was important only a very few people knew what was going on at Bletchley. 

MI5 was anxious to find out what Christie might know and questioned Knox, who insisted that she could not possibly know what was going on at Bletchley, the Telegraph reported. 

Christie’s novels sold tens of thousands at the time, so MI5 was anxious to find out what kind of information she possessed and where her knowledge came from. 

When the investigators questioned Knox, he insisted Christie couldn’t know anything about Enigma. They thought if they interrogated Christie themselves, it was bound to get out, so her friend Knox agreed to talk to the novelist. He invited her to his home and asked her why she had chosen to name her ‘fictional’ character major Bletchley. 

“Bletchley? My dear, I was stuck there on my way by train from Oxford to London and took revenge by giving the name to one of my least lovable characters,” Christie explained.

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