S10E01 - Five Little Pigs

Carla is engaged to be married but she is afraid that the fact that her mother killed her father will poison her husband's love for her, as he may fear that she has inherited a husband-killing tendency. Moreover, Carla remembers that her mother would never lie to her to hide an unpleasant truth and her mother told her she was innocent. That is enough for Carla but she wants Poirot to prove her mother's innocence to her husband to be.

Carla's father, painter Amyas Crayle, was murdered with a poison, coniine, which had been extracted from hemlock by Meredith Blake but subsequently apparently stolen from him by Carla's mother, Caroline Crayle. Caroline confessed to having stolen the poison, claiming that she had intended to use it to commit suicide. This poison ended up, however, in a glass from which Amyas had drunk cold beer, after complaining that 'everything tastes odd today'. Both the glass and the bottle of cold beer had been brought to him by Caroline. Her motive was clear: Amyas’s young model, and latest mistress Elsa Greer, had revealed that he was planning to divorce Caroline and marry her instead. This was a new development; though Amyas had frequently had mistresses and affairs he had never before shown any sign of wanting to leave Caroline.