A young widow is left in sole possession of her late husband's fortune, and her brother refuses to share it with her in-laws - so they enlist Poirot to try to prove that the widow's missing first husband might not be dead after all.
Source : http://www.imdb.com/title/tt0478227/
Lucy Crale enlists Poirot to investigate the fourteen-year-old murder case in which her mother was hanged for poisoning her philandering painter father. Source : http://www.imdb.com/title/tt0392952/
Elinor Carlisle seems to be the obvious murderer of her ailing aunt and the beautiful romantic rival who broke up her engagement, but Poirot uncovers darker motives. Source : http://www.imdb.com/title/tt0402444/
After Poirot pays a routine visit to his dentist, the doctor apparently shoots himself to death a short time later. Chief Inspector Japp appropriately recruits the detective as both witness and consultant. Source : http://www.imdb.com/title/tt0182352/