Like in the novel, he does this, finally, by gatecrashing an orgy where everyone is masked, until he is chased out, while a mysterious woman pledges to take his guilt upon her.
The biggest difference between film and original story and its greatest weakness is that Kubrick has added the figure of Ziegler, the wealthy patient of Bill who gives the party at the start where both Bill and Alice flirt with other partners - until Bill is urgently called up in his capacity of a doctor. For one party was not enough for Ziegler: while his guests were dancing downstairs, he had a private "dance" with a hooker upstairs, but she needs medical attention after she takes an overdose of drugs.
And at the end of the film Ziegler calls Bill to his house and sternly warns him not to pursue his investigations into the secret group that held the orgy the previous day. Ziegler himself is a member, and he tells how Bill was found out: because he arrived in a taxi while all the real members came in their limo's.
Ziegler also divulges that the girl who saved Bill at the orgy was the hooker who overdosed at his party. She is indeed dead, but not because she has been punished for helping Bill - that was only staged. She has died afterwards because she took another overdose...
Although he on purpose leaves some room open for doubt, in this way Kubrick gives a neat explanation for all the mysteries. Too neat - he explains away the mystery that Schnitzler on purpose left intact. The novella is so haunting exactly because there is no rational explanation, because all could well be a dream. That important aspect is somewhat lost in the film.
Some other changes, while we are at it:
- In addition to relocating the story from Vienna in the 1900s to New York City in the 1990s, Kubrick changed the time-frame of Schnitzler's story from Mardi Gras to Christmas. Happily, there are no Christmas songs blaring through the speakers, Kubrick must have used this season because it allowed him to have every set suffused with the dreamlike, hazy glow of colored lights... a filmic way to call up a dreamlike atmosphere.
- The character of Bill Harford is fundamentally more strait-laced than his counterpart, Fridolin. Bill sleep-walks through life with no deeper awareness.
- In the film, when Bill visits the prostitute ("Mandy"), he kisses her - contrary to the novel - and then is shocked into reality by a call from his wife on his mobile phone. This makes him leave. The next day, he makes a second visit to the room of the prostitute and then meets her room mate who tells him Mandy has tested positive for AIDS.
Some things which work particularly well in the film (while not present in the novel):
- the color scheme and the fairy-tale lights.
- the Venetian masks worn by the revelers at the orgy.
- the transposition of the evil world to that of the extremely rich - the real pornography in the film is that of money. Christmas has purely become a feast of consumption. But behind the glittering facade lurk exploitation and death.
My evaluation: 8.5 points out of 10 for the Venetian masks.
Detailed comparison of film and novel. Notes on both. Review by Lee Siegel. NYTimes review. Senses of Cinema. Reverse Shot. DVD Talk. BFI.