Love triangle

A love triangle involves three (or more) people. The typical love triangle in a story by Agatha Christie involves one person in a relationship falling for another person. This affection can be genuine, but it can also be false. The third part in the triangle is often looked upon with either sympathy or pity by others.

Love triangles in the works by Agatha Christie, and the persons involved

 * Death on the Nile - Linnet Doyle, Simon Doyle, Jacqueline de Bellefort.
 * Evil Under the Sun - Arlena Marshall, Patrick Redfern and Christine Redfern (and to some extent Kenneth Marshall).
 * Five Little Pigs - Amyas Crale, Caroline Crale and Elsa Greer.
 * The Hollow - Gerda Christow, John Christow, Henrietta Savernake.
 * The Mysterious Affair at Styles - Emily Inglethorp, Alfred Inglethorp and Evelyn Howard.
 * Sad Cypress - Roddy Welman, Elinor Carlisle and Mary Gerrard.
 * Towards Zero - Nevile Strange, Kay Strange and Audrey Strange.
 * Triangle at Rhodes - Valentine Chantry, Douglas Gold and Marjorie Gold (and to some extent Tony Chantry).
 * The Murder on the Links - Jack Renauld, Marthe Daubreuil and Bella Duveen (only to some extent, as Jack was vocal about not being in love with Marthe Daubreuil anymore)
 * Within a Wall - Alan Everard, Isobel Loring and Jane Haworth.
 * Wasps' Nest - Claude Langton, Molly Deane and John Harrison.

Non-canonical

 * The Mystery of the Blue Train (Agatha Christie's Poirot episode) - Derek Kettering, Ruth Kettering, Comte de la Roche (in the original version, Mirelle was involved too)
 * Le miroir se brisa (Les Petits Meurtres d'Agatha Christie) - Blanche Dulac, Marc Borel and Sylvia Franco (Sylvia Franco's original character wasn't involved with Marc in any romantic way)
 * Meurtre á la kermesse (Les Petits Meurtres d'Agatha Christie) - Catherine Dravignan, Olga Semiroff and Xavier Tremens (and Alice Avril to some extent)