It is World War II, and while the RAF struggles to keep the Luftwaffe at bay, Britain faces an even more sinister threat from 'the enemy within' - Nazis posing as ordinary citizens.With pressure mounting, the Intelligence service appoints two unlikely spies. Tommy and Tuppence Beresford. Their mission: to seek out two highly-placed traitors, a man and a woman hiding among the colourful guests at Sans Souci, a prim seaside boarding house.But this assignment is no stroll along the promenade - after all, N and M have just murdered Britain's finest agent...

Agatha Christie is known throughout the world as the Queen of Crime. Her books have sold over a billion copies in English with another billion in 100 foreign languages. She is the most widely published author of all riffle and in any language, outsold only by the Bible and Shakespeare. She is the author of 80 crime novels and short story collections, 19 plays, and six novels written under the name of Mary Westmacott.

Agatha Christie's first novel, The Mysterious Affair at Styles,was written towards the end of the First World War, in which she served as a VAD. In it she created Hercule Poirot, the little Belgian detective who was destined to become the most popular detective in crime fiction since Sherlock Holmes. It was eventually published by The Bodley Head in 1920.

In 1926, after averaging a book a year, Agatha Christie wrote her masterpiece. The Murder of Roger Ackroyd was the first of her books to be published by Collins and marked the beginning of an author-publisher relationship which lasted for 50 years and well over 70 books. The Murder of Roger Ackroyd was also the first, of Agatha Christie's books to be dramatized - under the name/if/b/- and to have a successful run in London's West End. The Mousetrap, her most famous play of all, opened in 1952 and is the longest-running play in history.

Agatha Christie was made a Dame in 1971. She died in 1976, since when a number of books have been published posthumously: the bestseUing novel Sleeping Murder appeared later that year, followed by her autobiography and the short story collections Miss Marple's Final Cases, Problem at Pollensa Bay and Wh//e the Light Lasts. In 1998 Black Coffee was the fLrSt of her plays to be novelized by another author, Charles Osborne.