seen as un-English (such as Oliver Manders in Three Act Tragedy), but they are rarely the culprits. Other detectives In addition to Poirot and Marple, Christie also created amateur detectives Thomas Beresford and his wife, Prudence "Tuppence" née Cowley, who appear in four novels and one collection of short stories published between 1922 and 1974. Unlike her other sleuths, the Beresfords were only in their early twenties when introduced in The Secret Adversary, and were allowed to age alongside their creator. She treated their stories with a lighter touch, giving them a "dash and verve" which was not universally admired by critics. Their last adventure, Postern of Fate, was Christie's last novel. Harley Quin was "easily the most unorthodox" of Christie's fictional detectives. Inspired by Christie's affection for the figures from the Harlequinade, the semi-supernatural Quin always works with an elderly, conventional man called Satterthwaite. The pair appear in 14 short stories, 12 of which were collected in 1930 as The Mysterious Mr. Quin. Mallowan described these tales as "detection in a fanciful vein, touching on the fairy story, a natural product of Agatha's peculiar imagination". Satterthwaite also appears in a novel, Three Act Tragedy, and a short story, "Dead Man's Mirror", both of which feature Poirot. Another of her lesser-known characters is Parker Pyne, a retired civil servant who assists unhappy people in an unconventional manner. The 12 short stories which introduced him, Parker Pyne Investigates (1934), are best remembered for "The Case of the Discontented Soldier", which features Ariadne Oliver, "an amusing and satirical self-portrait of Agatha Christie". Over the ensuing decades, Oliver reappeared in seven novels. In most of them she assists Poirot. Plays In 1928, Michael Morton adapted The Murder of Roger Ackroyd for the stage under the title Alibi. The play enjoyed a respectable run, but Christie disliked the changes made to her work and, in future, preferred to write for the theatre herself. The first of her own stage works was Black Coffee, which received good reviews when it opened in the West End in late 1930. She followed this up with adaptations of her detective novels: And Then There Were None in 1943, Appointment with Death in 1945, and The Hollow in 1951. In the 1950s, "the theatre ... engaged much of Agatha's attention." She next adapted her short radio play into The Mousetrap, which premiered in the West End in 1952, produced