Agatha Christie wrote twelve short stories in the locked room mystery genre. Only one of these, The Dream, was included in the sample of such mysteries which I have been analyzing thus far. All were written in the Golden Age with the exception of Greenshaw’s Folly published in 1956.

Seven of the stories feature Hercule Poirot, four feature Miss Marple and one is a Mr Quin story.

If we compare her solutions with those used in the wider sample we find, not unsurprisingly that her most common solution is the murder from the outside, which she uses in a third of her stories. This is very much in line with the general usage of this type of solution.

Contrary to expectations, given her known expertise in the field of poisons and the fact that she uses poisons as the most common means for her murderers to kill their victims if we look at the totality of her works (see chapters two and three), we find that she uses poison as her solution for in only one of her locked room mysteries. This, again, keeps her very much in line with the general low usage of poison as a method – though as we saw in chapter nine, this is at odds with the approach taken by other women writers who resort to poison in more than a quarter of all their locked room mysteries.

Where Christie differs markedly from the general position is in her use – or rather the lack of it – of mechanical traps in her locked room mysteries. She never uses this device even though it is the second most favoured approach used by writers in the genre generally.

In contrast, the solution which Agatha uses much more than the general case is the plot where the murderer kills his victim then contrives to enter and leave the locked room so that witnesses are convinced he or she could not have done it owing to the timings. Perhaps she felt more comfortable managing the complexities of deciding a precisely timed sequence of events than dreaming up the complexities of a mechanical device. Mechanical competence was not something that was generally required of, or therefore found, in women of her generation and class.

Christie did, however, utilise a wide variety of possible solutions. In the dozen locked mystery stories she wrote, she employed seven out of the ten categories (and six out of Dickson Carr’s original seven types). Bearing in mind that she was writing in the Golden Age (i.e. before the “other” category’s first appearance) she showed remarkable inventiveness to produce such a range of very different types of solution in what must be regarded as a genre in which she was not a prolific producer of output – compared to, say, Dickson Carr.

An intriguing feature too, of the distribution of her solutions, is that all the four Miss Marple stories each employs a different type of solution whereas, of the seven Poirot stories, three, i.e. nearly half, employ the same type of solution. Furthermore, her use of an unbreakable alibi solution pre-dates the first appearance of such a solution in the general sample by more than a decade.

Perhaps one of the reasons why she reigns supreme as the Queen of Crime is that she consistently found new ways to baffle her readers and kept herself ahead of the game even in genres, such as the locked room mystery, where she was not regarded as particularly specialist.