You’ve got to hand it to playwright Michael Hollinger. At a time when classical CD sales are minuscule and shrinking, when most Americans couldn’t tell you the difference between a violin and a viola, when once-famous names like Heifetz, Menuhin and Stern are virtually unknown except to music students, he writes a play about a string quartet that’s not only entertaining but, at times, gripping.

Who would have guessed that a drama about four string players could feature rivalry, violence, mental illness and romance? Who would expect that one of the characters in the play would assert that two others will never have a sexual relationship because “if you do I’ll cut your dick off”? Opus may not have any grand vision about the musician’s art, but it’s intelligent, suspenseful, funny and, most of all, convincing. Its real subject is politics — the politics of chamber music. The wonder, it turns out, is that the music happens at all.