Susan Ryeland, running a struggling hotel in Crete with her fiancé Andreas, is approached by Lawrence and Pauline Treherne, owners of Branlow Hall, a hotel in England. The Trehernes explain that a murder occurred eight years earlier at their hotel. Susan's former client, mystery author Alan Conway, used the events as the basis for his mystery novel, Atticus Pünd Takes the Case.

The Trehernes' daughter Cecily called her parents after reading the book, telling them that the book proves that the man in jail for the murder, Stefan Codrescu, is innocent. Shortly after that phone call, Cecily disappeared. Susan accepts an offer of ten thousand pounds to return to England, stay at their hotel, and use any insight she may have gained by editing the book to find Cecily and the true killer of Frank Parris.

Susan analyzes the novel closely and uncovers both the true killer of eight years earlier and where Cecily is. In a meeting at Branlow Hall Hotel, with the Treherne family and the police detective, Susan reveals the murderer as Cecily's husband, Aiden. Aiden had previously been a male prostitute and had left this life after meeting Cecily, who he had married not out of love but because of their home and his job at the hotel. When Frank Parris stayed at the hotel, he attempted to blackmail Aiden about his past. Aiden murdered Parris and, when Cecily discovered what Aiden had done, he murdered her as well.

Soon after confessing every detail, Aiden escapes the police detective and commits suicide by jumping in front of a train.

The novel also contains the complete text of Atticus Pünd Takes the Case, and readers can see where the fictional author Conway left clues throughout pointing to the "real-life" crime.

This novel was well received, with strongly positive reviews from published reviewers.

Michael Dirda writing in The Washington Post calls this novel one of the “metafictional mysteries” by Horowitz. The plot is complex while the writing moves at a brisk pace. The structure of this literal “novel within a novel” is presented clearly in the review, indicating one aspect of complexity of the plot.^[4]

Publishers Weekly considered it “a flawless update of classic golden age whodunits.”^[3]

Kirkus Reviews noted all the same features of the complex plot and clear prose, yet felt it was “over the top”: “The novel within a novel is so extensive and absorbing on its own, in fact, that all but the brainiest armchair detectives are likely to find it a serious distraction from the mystery to which it’s supposed to offer the key.“ Thus does Kirkus Reviews limit the audience of this novel to only the brainiest readers.^[5]

Sarah Lyall writing in The New York Times remarked it as a classic golden-age mystery novel, with a modern or postmodern take, and was impressed by the continual flow of high quality writing from the author. This novel was “a richly plotted, head-spinning novel about a present-day disappearance, a murder eight years earlier and a fictional murder that may be relevant to both.”^[2]

Moonflower Murders earned a "Rave" rating from the book review aggregator Book Marks based on six independent reviews.^[6] The six reviews include the four highlighted above, plus a review in The Wall Street Journal by Tom Nolan and a review by Beth Kanell in the New York Journal of Books. Extracts from the six reviews are posted, with links to the full reviews. Four reviews were marked Rave, one Positive and one Mixed.

In 2023 BBC began filming a series based on Moonflower Murders, expected to release in early 2024. Lesley Manville and Timothy McMullan reprised their roles as Susan and Atticus from the previous Magpie Murders series.^[7]

• Official website