After The Act of Roger Murgatroyd and A Mysterious Affair of Style, it is the third book in the Evadne Mount trilogy.

The book is presented in the form of a (fictional) memoir written by a British author called Gilbert Adair who has recently published two successful whodunits featuring mystery writer turned amateur sleuth Evadne Mount entitled The Act of Roger Murgatroyd and A Mysterious Affair of Style.

While he is staying there, two unexpected things happen: firstly, Anglo-Bulgarian novelist and essayist Gustav Slavorigin, the star of the festival, is murdered; and secondly, to his great surprise, Adair discovers Evadne Mount, the inspiration for his protagonist and the sharer of royalties from the two novels, sitting among the audience.

As opposed to the other novels in the trilogy, in And Then There Was No One there is a definitive shift away from the murder mystery and its solution toward "self-referentiality", toward the author and his or her problems.

In the years before his violent death, Slavorigin had been in hiding as he had published several essays critical of the United States and had therefore become, like Rushdie in reverse, the target of a fatwā-like edict pronounced by some obscure Texan multi-millionaire.