["Every Good Boy Deserves Favour"], a collaboration between Tom Stoppard, the playwright, and André Previn, the composer and conductor, is itself a theatrical pun—a play on words and music. This ingenious keyboard comedy … is about the political dissident as the discordant note in the orchestra that we call society.

In "Every Good Boy Deserves Favour"—the title is of course a mnemonic—a political dissident shares a room in a mental hospital with a madman who thinks that he has a symphony orchestra at his fingertips. The orchestra is a figment of his, and of our, imagination…. It is Mr. Stoppard's clever conceit that the orchestra performs at the madman's will, as the skeptical dissident stares in disbelief….

So much of the comedy comes from the contrast between the small reality—two men in a tiny cell—and the enormity of the delusion. Giving a lunatic an...