Harley Quin is an enigma. Even his friend Mr. Satterthwaite is unable to understand how the man seems to appear and disappear almost like a trick of light - and when he does appear it's usually in the sparkle of sunshine, or surrounded by a spectrum of coloured light pouring through a stained glass window.
Indeed, he is Harlequin. The only consistent thing about the mysterious Mr. Quin is that his presence is always a harbinger of love .. or death.
Quin and Satterthwaite appear in a string of short stories by the incomparable Agatha Christie. She often said that some of them are among her personal favourites. They'll be yours too.