4.50 from paddington

A woman is murdered on a train. When Miss Marple calls her friend Lucy Eyelesbarrow and asks her to disguise themselves to investigate, Lucy quickly accepted the challenge. Who is the dead woman? What was the motive for the murder? And why the body was thrown off the train and later hidden in Rutherford Hall? When the second murder occurs, everyone in Rutherford Hall feel in danger, then Miss Marple sets up a trap to catch the killer..