Nick Nightingale (SPOILERS)

During their exchange, Ziegler is symbolically closing Bill's eyes, returning him to an unseen state. Ziegler gives his placating interpretation of the events, reassuring Bill that everything is fine, but warns that he best not tread further.

He agrees, and now has his eyes wide shut.

Why does Bill go to Ziegler’s party every year? On one hand we can say that he is networking, hoping to add wealthy clientele. On the other hand, we can see that Bill wants to fit in. He wants to be a part of the elite of which Ziegler is also a part of, yet he can't. There is a running motif throughout the film pertaining to money. Although Bill is frequently seen physically handling money throughout the film, the clearest example is obviously Bill’s name, referring to a banknote or invoice. In the opening sequence we hear Bill ask Alice whether or not she has seen his wallet. During Bill’s dialogue with Nick at the party, he asks him why he ever left medical school, subtly indicating how the prospect has increased his overall status, both financially and socially (e.g., Alice as a trophy wife; relationship with Ziegler). In other words, the career of a physician has brought him to the apex of the pecking order. He is now in the company of Ziegler, unlike Nick, whose status is that of servant.

But even though Bill is of considerable wealth, he is not part of the elite. He rents out his costume for the mansion, and instead of driving in a limousine, takes a cab. This point is made clearly following the party sequence in the beginning. At the party, those of status are wearing black, while those who are entertainers (e.g., Nick and orchestra) are in white. In the scene following the party, we see Bill in his office wearing a white coat, mirroring the white worn by the entertainers the night before. Bill is part of the same servant class as Nick, only in a different format.