The Mysterious Mr. Quin

First published in 1930, ''The Mysterious Mr. Quin'' is a collection of twelve interconnected stories by Agatha Christie featuring the enigmatic Harley Quin and his associate, Mr. Satterthwaite. Unlike her typical whodunits, these tales have a slightly supernatural, romantic, and darker edge, with Quin appearing mysteriously to help solve old, emotional mysteries.

Mr. Harley Quin is an otherworldly, almost magical figure who appears, often with a trick of light, to act as an "advocate for the dead" or a "friend to lovers". Mr. Satterthwaite is an elderly, observant, and wealthy man who serves as the "looker-on at life" and is often guided by Quin to solve the mystery.

The stories are mostly self-contained but build upon each other, with Mr. Satterthwaite frequently recognizing Quin as a "catalyst" for revealing the truth behind past crimes or tragic events.

The stories focus on resolving past, often tragic, emotional secrets rather than traditional "who-caught-the-killer" mysteries, and Quin often helps right past wrongs.

Agatha Christie herself noted that these stories were among her favorites.