Hercule Poirot and Jane Marple are the detectives of Agatha Christie known to millions; somewhat less well known are Tuppence and Tommy Beresford and Inspector Battle. In all four cases, Christie wrote novels, as well as short stories, using these characters. However, there are two other Christie "detectives" who never appear in a novel, only in short stories. The quotation marks are necessary, for neither of these men fulfill the usual image of the British detective. They are Mr. C. Parker Pyne and Mr. Harley Quin. With the latter must be included his friend Mr. Satterthwaite…. The stories of Pyne and Quin illustrate two different elements of Christie's mystery fiction—elements that are not part of her works about the other detectives. In the Pyne stories she combines detection, or at least deduction, and the manipulation of human lives to achieve their happiness, while in the Quin stories she combines detection and fantasy.

There are fourteen Parker Pyne stories. Of these seven can hardly be called detective stories; rather they are cases in which Pyne manipulates people to give them the happiness they desire—the mystery element is how he accomplishes the task. The other seven involve detection by Pyne when he is asked to help an unhappy person. (p. 110)

As a result of Pyne's omnipotence, Christie's stories about him can be considered improbable. His ingenious schemes to provide people happiness by manipulating their views of their world, his astounding ability at classification, and his insight into human character based upon that classification are far beyond the powers of most people. The improbability is lessened, however, by the nature of most of his cases. They are human interest stories, dealing with problems that face most people: problems of love, boredom, and money. Also, Pyne has none of the usual eccentricities of so many English detectives of the period in which he was created; rather, he is presented as an "ordinary," elderly English middle-class man in his tastes and personal life. It is in the blending of improbable action and ordinary characters that these stories are distinctive.

If Parker Pyne is omnipotent in his cases, Harley Quin is omniscient in the thirteen stories in which he appears, though he denies it….

Quin is based upon the harlequin of the English pantomime, which is a descendant of the sixteenth-century commedia dell'arte…. Harlequin was not originally a supernatural character, but by the nineteenth century, he and Columbine, as presented on the English stage, had become fairylike creatures not bound by time and space. (p. 112)

The resemblance to motley and the eerie effect of light on his appearance conjoin the elements of the stage harlequin and the supernatural being within Quin.

However, other characteristics of the supernatural are included in his presentation. The most obvious are his sudden appearances and disappearances…. (p. 113)

[One] cannot discuss Quin without including his mortal partner, Mr. Satterthwaite. (p. 114)

Quin and Satterthwaite are a team, a matching of the supernatural and the human—surely one of the most unusual detective teams in fiction….

Neither Quin nor Pyne will ever have the popularity of Poirot, Marple, or the Beresfords. The short story form does not allow for the development of character which the novel does. Apparently, Christie did not see her way to extending Pyne's manipulation of people or the supernatural characteristics of Quin to the length of a novel…. Though Pyle is a basically colorless figure, the disquieting Quin and the little dried-up Satterthwaite are difficult to forget, and one can only regret her abandonment of them. But whatever one may think of the characters and the stories in which they appear, the fact remains that the twenty seven stories are significant examples of Christie's experimentation in adding narrative interest to the detective genre by employing elements not generally considered compatible with it. (p. 115)