4:50 from Paddington

While traveling on a train from Paddington Station, Elspeth McGillicuddy witnesses a murder in a passing train.

When the authorities dismiss her story due to lack of evidence, she enlists the help of her friend, Miss Marple.

Miss Marple, unable to investigate personally, hires Lucy Eyelesbarrow, a resourceful and intelligent young woman, to infiltrate the Crackenthorpe family, who live near where the crime occurred.

Lucy takes on a domestic role in the household.

As Lucy uncovers the family's secrets and resentments, Miss Marple guides her from afar, piecing together the evidence and revealing a complex plot of greed, hidden identities, and long-held grudges.