The name of the manor house where Miss Jane Marple conducts her inquiries is called Rutherford Hall in Dame Agatha Christie's 1957 novel. It was changed to Ackenthorpe in this movie to avoid comparison with the surname of Dame Margaret Rutherford (Miss Jane Marple).
The character of Miss Jane Marple's librarian friend, Jim Stringer, was not part of the original story (and never featured in any of the Christie books). The part was written for Stringer Davis, who was married to Dame Margaret Rutherford.
Despite privately remaining unimpressed by the film, Agatha Christie dedicated her 1962 novel "The Mirror Crack'd From Side to Side" to Margaret Rutherford "in admiration".
This adaptation of Agatha Christie's 1957 novel actually gives Miss Marple far more to do than the original. In the book, it is not Miss Marple, but her friend Mrs. McGillicuddy, who witnesses the murder on the passing train, whilst it is the much younger Lucy Eylesbarrow who obtains the job at the old house (as housekeeper rather than maid) to spy on the family. Both of these important characters are omitted entirely from the film. In the book, the family is called "Crackenthorpe" instead of "Ackenthorpe".
This movie was a success at the box-office, earning MGM a profit of $342,000 ($3.29M in 2022) according to studio records. Rather more remarkably, it was the studio's biggest success in what was a very lackluster year, financially.