"The Case of the Distressed Lady."
(a.k.a. "The Cat and the Chestnut").
By Agatha Christie (1890-1976).
First appearance: Cosmopolitan, August 1932 (as "The Pretty Girl Who Wanted a Ring").
Reprinted in Woman’s Pictorial, October 22, 1932 (as "Faked!").
Collected in Parker Pyne Investigates (1934; U.S. title: Mr. Parker Pyne, Detective).
No media adaptations so far.
Short story (15 pages).
Online at Archive.org (HERE; EPUB).
     ". . . I have had a long experience in the compilation of statistics. From that experience I can assure you that in eighty-seven percent of cases dishonesty does not pay. Eighty-seven percent. Think of it!"

In his unflagging effort to make his clients happy, as per his advert, Parker Pyne foils a criminal plot, even though it still earns him an unjustified "You oily old brute!"

Characters:
~ Mr. Parker Pyne:
  An expert at repairing relationships.
~ Daphne St. John:
  A lachrymose lady with a self-inflicted problem.
~ Claude Luttrell and Madeleine de Sara:
  ". . . one of the handsomest specimens of lounge lizard to be found in England" and "the most seductive of vamps."
~ Lady Dortheimer and Sir Reuben:
  Blissfully unaware that they're the designated victims.

Resources:
- Concerning Parker Pyne, consult Wikipedia (HERE), Hercule Poirot Central (HERE), and Wikipedia again (HERE; WARNING! SPOILERS).
- It has been nearly two and a half years since we last dealt with Agatha Christie at any length, "The Plymouth Express Affair" (HERE) being the featured story then.

The bottom line:

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~