What is the full name of the person who realizes that she has killed herself?
Successful mystery novelist Janet Frobisher, who has been separated for years from her husband, a man with a criminal past, lives in an isolated home in Northern England. Her nearest neighbour is nosy veterinarian Dr. Henderson. Janet has an affair with, and falls in love with, her secretary Chris' fiancé, Larry, who is years younger than she. 
When her estranged husband unexpectedly appears, Janet poisons him by administering medication given to her by Dr. Henderson for her horse. One of the deceased man's criminal cohorts arrives as she's preparing to dispose of the body in the local lake. When Frobisher's secretary and Larry arrive at the secluded house, the mysterious man, who has assisted her with her scheme, impersonates George, the long-absent spouse of Janet.
George and Janet trade accusations and insults. Chris learns of Larry's affair with Janet, and determines to leave for London. Janet tries to convince Larry to stay with her, but he loves Chris and chases after her unsuccessfully. George shoots Janet's horse to upset her. Janet pretends she is remorseful about Larry and Chris, and sends George after Chris in an unsafe vehicle. He crashes, but survives. 
The next morning the authorities are dragging the lake because of the crash. Janet's attempt to kill George has trapped them both, although George plans simply to run away. Janet tricks George into poisoning himself. As George dies, Dr. Henderson arrives and says he knew all along that George was an imposter; the real George stopped by his house in the fog the night he arrived. Janet pretends to faint. Dr. Henderson gives her a drink from the same flask she used to trick George. When she opens her eyes and recognises the flask, she realises she has killed herself, and bursts into laughter.
Janet Frobisher