Agatha Christie’s name is synonymous with the mystery novel, and her books have been translated into more than one hundred languages. Almost all of her novels remain in print. Although some critics consider her work to be no more than popular fiction, the mystery novel has become an increasingly respectable literary genre. Critical studies have been devoted to many aspects of the field, in particular to Christie, one of the finest writers of the classic detective tale.

The traditional mystery story has a particular set of rules, in which the writer sets a puzzle, provides clues for the reader to follow, and then delivers a solution to the puzzle that is both a surprise to the reader and consistent with the accumulated evidence of the story. The Mousetrap provides a perfect illustration of how Christie did precisely that and at the same time found new ways to combine those elements.

The Mousetrap, originally the short story “Three Blind Mice,” which was adapted first into a radio drama and then into a full-length play, contains many Christie trademarks. One of these is the setting, which, as in most of her works, is the English countryside. Yet this frequently serves as little more than a backdrop. Christie likes to cut the setting—and thus the characters—off from the rest of the world so as to create a closed circle of suspects. In Ten Little Indians (1943), the characters are stranded on an island; in Murder on the Orient Express (1934), they are traveling on a train; and in many of the stories, including Christie’s first novel, The Mysterious Affair at Styles: A Detective Story (1920), they are gathered together in a country house. The Mousetrap re-creates this setting with the Great Hall at Monkswell Manor. Christie assembles her characters and then isolates them with a snowstorm; from that point on, the outside world no longer intrudes. There is no mention of politics or names and events in the news. Political realities do not exist, except in the most general of terms; Mrs. Boyle accuses Miss Casewell of being a Socialist, and she laments the lack of responsibility of the lower classes. The play’s reality, its true setting, is a tightly closed circle of individuals.

In this world, plot development is paramount. Every narrative detail and character description serves to move the drama forward. In fact, Christie deleted the first nine pages of an early draft of the play, where the murder had been described at greater length, to focus more quickly on the narrow circle and the puzzle. The curtain opens on a dark stage and the audience hears shrill whistling, a scream, and police whistles. The lights go up to a radio broadcast account of the murder in an empty room; the announcer adds that a heavy snowstorm is descending on the English countryside. Before a single actor has even been seen, the audience is caught up in the middle of the puzzle.

The stage directions for the play are detailed, since much of the action depends on staging. Red herrings are thrown to the audience with both sight and sound clues. Mollie’s glove contains a London bus ticket; Christopher Wren wanders about mysteriously, whistling a succession of nursery rhymes. Gestures, looks, silences, all are designed to focus suspicion on one character after another. These bits of misdirection are carefully designed to hide the clues that reveal the true murderer.

Critics have pointed out the lack of character development in Christie’s books, but this is a deliberate device designed to keep attention on the puzzle. Character development would interfere with the...