Miss Marple. A Murder is Announced. Episode 3

Miss Marple explains that Letitia died of pneumonia in Switzerland. Aware that Letitia was in line to inherit a fortune, Charlotte posed as her deceased sister and returned to England a year earlier, in a village where few people knew her. She avoided people who knew Letitia well, like Belle Goedler, and covered her throat with strings of pearls to hide the scars from her surgery. Rudi Scherz had innocently recognized her, having worked at the Swiss hospital where she had her surgery; Charlotte killed him to prevent him talking to anyone. She hired Scherz and had him put in the advertisement to gain witnesses. She oiled the door and frayed a lamp cord, which she later shorted by pouring water on it when everyone was distracted by the clock chiming, so the room would be suddenly dark. She had then come behind Scherz and shot him, cutting her own ear with nail scissors before returning. That night, she replaced the frayed lamp with a new one (shepherd vs. shepherdess, as Bunny said). Bunny knew both sisters from childhood. Charlotte had taken Bunny into her confidence about the inheritance but not about the murder of Scherz. Bunny sometimes called her "Lotty" (Charlotte) instead of "Letty" (Letitia); Charlotte feared that Bunny might thereby reveal the truth, so Charlotte had poisoned some aspirin tablets taken by Bunny. Amy Murgatroyd had realised that Miss Blacklock was the one person whose face was not illuminated by Rudi Scherz's torch; Charlotte had overheard Hinchcliffe and Murgatroyd's conversation, and killed Murgatroyd as soon as Hinchcliffe left.
Miss Marple persuaded Mitzi and Edmund to play parts in tripping up Charlotte Blacklock; Phillipa's admission to being Pip was not expected; Inspector Craddock kept up the act to claim Edmund was after Phillipa's money. Mitzi had agreed to serve as the bait, and Miss Marple imitated Bunny's voice to cause Charlotte to break down and confess.
Ultimately, Mitzi takes up a new post near Southampton. Phillipa and Emma inherit the Goedler fortune. Edmund and Phillipa marry and return to live in Chipping Cleghorn.