Like Ezra Chater, Captain Brice seems to be present in the play mainly for the more intellectually nimble characters to run circles around him, to their own (and the audience's) amusement. At first glance he could be the play's moral center. When he confronts Septimus about his affair with Mr. Chater, he uses the language of right and wrong:
BRICE: Look to your honour, sir! If you cannot attend to me without this foolery, nominate your second who might settle the business as between gentlemen. (1.3)
"Honour," "gentlemen"...Captain Brice sounds like a fine, upstanding guy, just trying to keep high standards in a sick, sad world, right? Totally not like that skeevy Septimus, who's having an affair with Mrs. Chater behind her husband's back... Oh wait, Brice is doing that too. While Brice uses the language of morality, his actions speak louder than his words. One could even argue that his hypocrisy, and his eagerness to get poor old Mr. Chater to face an armed Septimus, makes his behavior morally worse than Septimus's own shenanigans. By making Brice such a two-face, the play forces us to come up with our own moral judgment of the actions of its characters, rather than offering a clear-cut division between right and wrong.