It ought to have been an open-and-shut case. In the small hours of July 10, 1923, as a brutal heatwave was finally broken by a thunderstorm that shook London to its core, the 32-year-old French wife of a wealthy young playboy gunned down her husband outside their suite in the Savoy Hotel. The shooting was the violent culmination of a nine-day stay during which the serially faithless wife and the jealous husband had rowed repeatedly.
British law, unlike that of France, admitted no defence of crime passionnel to the act of murder and, when the curtain rose two months later on the sensational trial that followed at the Old Bailey, there was every expectation that the accused would follow in the footsteps of Edith Thompson, a British woman who earlier that year had found herself in the same dock for killing her husband and who subsequently had been hanged at Holloway Prison. But there would be no noose for the Savoy killer. The former Marguerite Alibert had one thing going for her that the late Mrs Thompson had not: the unfortunate target of the three .32 bullets "accidentally" fired from the black Browning semi-automatic pistol she kept under her pillow was an Arab.
A new book about the case argues that the accused succeeded in her plea of not guilty to the murder of Ali Kamel Fahmy thanks to a perversion of the course of justice engineered by aides to the British royal family.
It's a tempting theory and one developed with great enthusiasm and skill by the British author, Andrew Rose.
An Old Bailey barrister, he revisits a story he first told in 1991, armed with the fresh knowledge that during the First World War Marguerite - or Maggie Meller, as the high-class prostitute was then known in the French demimonde - had had a brief affair in 1917 with the young Prince Edward VIII, heir to the British throne.
Edward, a dissolute disappointment who in 1936 was to shock Britain and the Empire by abdicating in order to wed Mrs Wallis Simpson, an American divorcée, was sufficiently dull of wit to have showered the object of his wartime affections with a series of highly indiscreet letters. These, it seemed, remained in Marguerite's possession, and it is the revelation that they did so that has led Rose to construct an entertaining and almost plausible conspiracy theory.
It boils down to an agreement having been made between Marguerite and the royal household which, asserts Rose, "colluded with the Director of Public Prosecutions and the trial judge" in what amounted to "a conspiracy to pervert the course of justice".
The evidence? Unlike the murder scene at the Savoy, there is no smoking gun for Rose's theory, merely, in his own words, "a wealth of coincidence". What is certain, however - as evidenced by court records and newspaper reports at the time - is that Marguerite's greatest advocate at the Old Bailey was racial prejudice.
Marguerite was born in Paris in 1890, the daughter of a cab driver and a cleaning woman. After an early pregnancy, as a teenager she found work as a prostitute in the French capital and set about securing herself the financial support of wealthy men.
In 1907, aged 17, she met André Meller, the rich (and married) 40-year-old son of a Bordeaux wine merchant and, during a seven-year affair, she acquired all the trappings of the kept woman while continuing a series of profitable affairs with a string of other, equally generous married men.