On 14 May 1945, just days after the Nazi surrender, a British officer dug up a metal canister in the grounds of a German country estate. Inside the canister he found reels of microfilm which later translated to 9,725 pages of secret Nazi files.
Among the sensational documents was the correspondence relating to a curious wartime episode involving the Duke and Duchess of Windsor. So explosive was this material considered to be that for the next 12 years it was kept hidden in a folder known as the Windsor File, its contents revealed only to prime ministers, US presidents and officials sworn to secrecy.
Andrew Morton's new book takes us into Da Vinci Code territory as he promises to uncover the saga of the file for the first time, calling it "a royal story the establishment tried to ban".
But before we get to any juicy revelations we must first go over the familiar ground of the king who gave up his throne to marry Wallis Simpson. Morton, who scored a remarkable scoop in 1992 with Diana, Her True Story, spices up the drama with descriptions of the young Prince Edward's dark depression and threats of suicide before he meets the married woman he believes can save him.
It was in London during the 1930s that Wallis and the prince first came into contact with senior Nazis. Among their circle was Joachim von Ribbentrop, the German foreign minister who took a shine to Wallis, at one point ordering daily bouquets of 17 carnations to be delivered to her door (rumoured to signify the number of times they slept together). The prince, meanwhile, took a keen interest in Hitler's rise, seeing his policies as the key to Germany's prosperity. In October 1937, less than a year after the abdication, the now Duke and Duchess of Windsor made an unofficial tour of Germany, dining with Goebbels and Hess and meeting the Führer at Berchtesgaden. But the duke was not alone in his admiration for the regime, and what Morton is searching for is hard evidence that he actually conspired with the enemy.
His best chance of proof, he believes, is in the notorious Windsor File. The documents relate to the summer of 1940 when the duke and duchess fled their home in France and made their way through neutral Spain to Portugal. During their stays in Madrid and Lisbon, German diplomats relayed back to Berlin tales of the couple's treasonous talk, particularly the duke's feeling that Britain would lose the war and that an early peace would be the country's best hope. But probably the nearest the duke came to collaborating was to ask the Nazis, via diplomats, to take care of his possessions in France.
The Germans in turn considered kidnapping the duke and keeping him in Spain as a useful negotiating tool. But after some firm words from Churchill the couple eventually left Lisbon for the Bahamas, where the duke spent the remainder of the war as the islands' governor.
Following the discovery of the microfilm the details of the Lisbon episode were considered so potentially damaging to the duke, and to the wider royal family, that Churchill and Clement Attlee attempted to have the Windsor File exempted from plans to publish the German archives.
Finally, however, the historians compiling the volumes got their way and the documents were released in 1957.
In the end the exposé did little damage to the duke, who continued his idle life of luxury until his death in 1972.
So has Morton uncovered anything new? The answer is no, but as damp squibs go he has managed to make a readable and occasionally racy fist of it.