Henry James's 1880 novel, Washington Square, was originally adapted into a play version entitled The Heiress by Ruth and Augutus Goetz in 1948 and eventually went on to become a film in 1949. The Heiress, directed by William Wyler, was extremely faithful to the play The Heiress. The play, on the other hand, was fairly faithful to Washington Square, but it did tone Dr. Sloper's arrogance down a bit and caused Catherine to lower herself into playing the same game that Morris Townsend played with her, causing the feel of the film and play to be a bit more sinister. Overall, the film adaptation of Washington Square was somewhat different from the book that it was based upon, but the sinister tone caused it to be just as good as (if not better than) Washington Square.
One of the reasons why this darker tone works for the film is due to the direction that Wyler gives the film. The character of Morris, as depicted by Montgomery Clift, comes off as being a sweet young man who is a bit guilty of being greedy, whereas in the book, he was shown as being a manipulative man capable of appearing to be sweet who was not really a good man at all. That is why when Catherine rejects Morris in the book, we are glad that she does this; but, in the film, we find this to be a rather dark and hateful action. If the actors had been even just a bit off in their acting, this dark tone would not be apparent throughout the film, but Wyler manages to keep the actors and actresses in line.
Another reason why this film succeeds is the musical score. Many people accuse this film's score of being repetitive and even dull. But, this musical score by Aaron Copland is what keeps this film's tone in check. The music is a bit repetitive, but it is in this repetitiveness that the cruelty of Catherine (Olivia de Havilland) and Dr. Sloper (Ralph Richardson) comes across to the audience. Without this score, the movie's flow would be interrupted if not obliterated.
Overall, this film is a most excellent adaptation of the play that it is based upon. The play itself is also a very good vision of the book that it is based upon because it manages to take the most important parts of the book and transform them into play material. The tone, which comes off in both the play and film as being more sinister, combines with the faster pace to make for a very good play and film.