Harley Quin is a mystery. He appears and disappears unexpectedly and by strange tricks of light and reflections; making his clothes seem brightly multicoloured like the theatrical Harlequin.

Parker Pyne made his debut in 1934 in the collection of short stories entitled Parker Pyne Investigates. Parker Pyne states quite clearly that he is not a detective: "I am, if you like to put it that way, a heart specialist".

A middle-aged woman and successful detective novelist; Ariadne Oliver is a feisty character who believes that Scotland Yard would be better run by a woman!