Agatha Christie's status as the queen of crime may be because of her ingenious plots, but her continuing popularity these days - especially with television producers - has more to do with something else: the decor.
Written between 1920 and 1968, Christie's novels are fixed in our imagination in an era which is 1920s or perhaps 1930s - but definitely "period". There is a charm in their set-pieces - the locked library, the French windows through which the maid overhears a quarrel, the footsteps on the gravel drive - and they are populated mostly by straightforward people, summed up by their creator with the sort of snap judgment which may contain an important clue.
"Annie is the house parlourmaid. A nice girl but an inveterate talker"; "He was well-groomed, with a cheerful, somewhat vacuous face. Not a type that I admire."
Then there is the dialogue, only distantly related to natural speech. "Sorry. I didn't mean to startle you. I didn't know there was anyone here"; "Father, I'm going up to town in the Hispano. I can't stand the monotony down here any longer."
On television, the gleaming cars, the cigarette holders, the backless frocks and the Marcel waves became part of the ritual; they allowed us to watch the unrolling of events a point or two above dozing.
Now this vision of Christie is under threat, from what she might have called a brash young American. Chorion Intellectual Properties, the holder of the Christie copyright, plans to bring some of her books up to date by setting them in "the microchip age", in the belief that "a modern setting will bring in a younger demographic".
Chorion also plans to "develop a licensing programme based on Christie's works and associated characters for the gift and collectable markets". But any upgrading of the technology would upset Christie's elaborate use of mechanical alibis, those intricate plots built up from chance overhearings and deceptions about time.
Seven digital clock radios would not do the same job as the ticking alarm clocks used in the Seven Dials Mystery. The Internet would provide Superintendent Battle of Scotland Yard with all the information he needed on subversive secret societies and all those letters - lost, hidden, delayed, read secretly - would be replaced by e-mail.
The very possibility of a mobile phone destroys the set-up for the telephone alibi - a Christie favourite. The phone call from an accomplice could not have been used to help the murderer in Lord Edgware Dies, and, if Lord Edgware had had a burglar alarm installed at his London Regent's Park house instead of a bolted door, many red herrings would have been avoided.
The staple plot device of the locked room needs old-fashioned things: locks, a library, maids. Just as the important motives of scandal, blackmail and secret pasts need a society with an agreed code of behaviour.
And there is, of course, a long list of supporting plot elements that simply no longer exist, from impassive butlers to steel millionaires to railways that stick to a timetable.
Chorion's gifts and collectables will also be full of difficulties. Unlike the characters in the Sherlock Holmes stories, who come with a range of accessories, the only Christie character with distinctive features (pear shape, bowler hat, moustache, spats) is Poirot. Apart from that, any franchising company would surely want those elaborate props - the oriental dagger, the box of poisoned chocolates, the clock that had been tampered with - that had been done away with in their updating.
If Christie is seen as ripe for commodification in the US, in Europe she is being deconstructed in an elegant but rigorous manner. Pierre Bayard, a psychoanalyst and a professor of literature at the University of Paris, has written a book, Who Killed Roger Ackroyd? (Fourth Estate), which casts doubt on whether Dr Sheppard really did murder the local squire.
The Murder of Roger Ackroyd (1926) is famous for having a narrator who turns out to be the murderer, having withheld vital information in his account of the happenings at the great house - a piece of narrative sleight of hand which has long fascinated the critics.
"If the narrator of every novel is suspect then we can no longer rely on any part of the text," concludes Bayard, perhaps with slight exaggeration. Christie's original solution is not only unlikely, he argues, it has no proper motive. Bayard is interested in why Christie should have made this "error"; he also finds a relationship between the detective story and the deeper mysteries of the human mind: "Solutions to plots mask real answers".
Christie was a tireless producer of material for the imagination. Her novels are so sparely written that the reader rushes to fill in the gaps, and one of the reasons she has had such a successful afterlife is that later generations of readers can interpret her books to their liking.
There have already been several academic examinations of her work. Like Chorion's plans to drag the novels into the 21st century, they are just another example of the fun to be had with icons of popular culture.