Agatha Christie's Miss Marple: Nemesis

Miss Marple's wealthy friend, Mr.Rafiel dies. He has left a clause in his will that if Miss Marple can solve a "certain crime" for him she will receive 20,000 pounds. He also states that the "code word" is Nemesis. Miss Marple could use the money, and therefore accepts. A month passes, and Miss Marple begins to worry. She has no clue what she is to do. That same day, she receives a letter from Mr. Rafiel, postmarked before his death, enclosed is a ticket to a tour of Manor Houses & Gardens. Miss Marple sets out on the tour to solve the mystery, unaware of what crime she is to investigate-but is there any doubt that it is MURDER?