Marple: Nemesis (2007)

Miss Marple is called upon to solve her most perplexing case yet. Upon his death, financier John Rafiel asks her to solve a murder. Only problem is that the murder may or may not have place as yet and the victim is unknown. All that he has given her is two tickets on the Daffodil Tour Company's Mystery Tour. It soon becomes obvious that others on the tour were also "selected" by Mr. Rafiel. Jane Marple, assisted by her nephew Raymond West, concludes that the case must be related to that of Verity Hunt, a young woman who in 1939 was running away from an overattentive landlord and eventually disappeared. When a member of the tour dies mysteriously, she also realizes that someone is desperate to keep a deep, dark secret.