Betsy and l'Empereur: did Napoleon escape St Helena?

Did Napoleon Bonaparte spend the last 16 years of his life living with an Englishwoman called Betsy, keeping bees on a plantation in Louisiana?

Did the British government do away with Napoleon for budgetary reasons? (The Gordon Browns of the day apparently begrudged the exorbitant cost of guarding him on a rock in the Atlantic.) Is the body inside the giant coffin in Les Invalides, Paris, visited by tens of thousands of people each year, really that of l'Empereur? Or is that of his valet, childhood friend and (alleged) illegitimate brother, Jean-Baptiste Cipriani?

From these intriguing questions – all of which have been posed by historians or conspiracy theorists at one time or another – Antoine de Caunes, actor, sometime presenter of Eurotrash and now film director, has woven a mystery film which opened in French cinemas and at the Berlin film festival last week.

Monsieur N, made with an exquisite attention to period detail, and a fine cast of French and British actors, is the latest contribution to one of France's occasional Napoleonmania bouts. It follows a four-part, mini-series on the life of Napoleon shown last year which was the most costly production ever made for French TV.

Although M de Caunes, 49, is best known in Britain and France as a mordant TV presenter and comic actor, his second full-length film is not a comedy. Nor is it a historic drama or a conspiracy film.

It is a thriller and a detective story, closely based on the real events and real characters in the last six years of Napoleon's life (or what are generally assumed to have been the last six years of his life) on the island of St Helena. Although the film refuses to offer a firm conclusion, it plays with the idea that Napoleon may have fallen in love with a young Englishwoman, Betsy Balcombe, faked his death in 1821 and escaped to live in idyllic obscurity on a plantation in Louisiana until around 1837.

M de Caunes says that the film sticks to historical reality in the detail and the bitchy interplay of characters, in Napoleon's "imperial court" at Longwood House in St Helena and his "last battle", against the humourless and rigid British governor, Sir Hudson Lowe (superbly played by Richard E Grant). But the story which the film spins from these truths is "pure imagination", M de Caunes says.

Or maybe not.

A young woman called Betsy Balcombe (played in the film by Siobhan Hewlett) did indeed live on St Helena from 1815-18. And she was indeed befriended by Napoleon (played in the film by Philippe Torreton).

Napoleon's valet, Jean-Baptiste Cipriani, who resembled him closely, died on the island in 1818. When his tomb was opened at the same time as Napoleon's in 1840, it was empty.

Some evidence suggests that Napoleon was poisoned, although it is far from clear that the British government was involved in the plot. Accusations have long circulated that the British stole Napoleon's body and buried it in Westminster Abbey, as a final act of pique.

M de Caunes' film follows the investigations of a fictional British lieutenant (played by Jay Rodan) who uncovers, 20 years later, evidence that Napoleon may have faked his own death by poisoning. The lieutenant concludes that Cipriani's body was substituted for that of the emperor, who had bribed the British governor to look the other way. Why and what happened next is left partly to the imagination of the film-goer.

Not entirely coincidentally, France's foremost Napoleonic scholar, Jean Tulard, who has written 40 books on the subject, has just published a new volume on the St Helena years: Napoléon et les mystères de Saint-Hélène.

M Tulard has praised the film for its convincing portrait of the characters, of Longwood House and its precise attention to detail of British and French uniforms. However, his book concludes, rather unromantically, that Napoleon did indeed die in St Helena on 5 May 1821, of stomach cancer, just as the official autopsy reported.