Someone just found the body of Leopold Reynolds, The Joyce younger brother drowned in the small brook.
Rowena, unusually upset about the death, informs Poirot she had seen him in the library the night of the party, and believes he witnessed his sister's killer. Poirot soon has a theory, and advises the police to search the woods near the quarry. The search turns up Olga's body in an abandoned well, having been stabbed.
With his theory, he already find out who is the killer of joyce Reynolds and he tells everyone to gather around to uncover the investigatio abou the murder of Joyce Reynold, Leopold Reynolds, Lesslie Farrier and Olga seminoff.
With his theory, Poirot tell everyone that rowena is the killer and he muses that Rowena would likely have shared a similar fate to Olga, as Garfield's motivation for the murder was his narcissistic desire to construct another perfect garden with Rowena's money; he would have had no further need of her, as she had already provided him with a Greek island she had secretly purchased.
Police bring the Michael Garfield to the room and let him confess about the murder that he and Rowena do a years ago.