Michael Hollinger is a professional playwright, which is to say he knows what he's doing -- and we've been watching him do it. Via City Theatre and the collaborating Arden Theatre in Philadelphia, Pittsburgh has had an up-close, stop-action perspective on his career, having seen the premiere of his "Incorruptible" (a medieval quasi-farce) in 1996 and then his "Red Herring" (a 1950s comedy) in 2001.

	Mark Garvin From left to right, Douglas Rees, Greg Wood, David Whalen, Patrick McNulty and Erika Cuenca star in "Opus." Click photo for larger image. 'Opus' Where: City Theatre, 13th and Bingham streets, South Side. When: Through April 9; 7 p.m. Tuesdays; 8 p.m. Wednesdays-Fridays; 5:30 and 9 p.m. Saturdays; 2 p.m. Sundays; 1 p.m. April 5. Tickets: $15-$40; 412-431-CITY.

Right on this same five-year schedule, Hollinger is back at City with the co-premiere of his "Opus," a drama with comic shading about the inner workings, musical and personal, of a string quartet. Directed by Terrence J. Nolen of Arden, where it was performed first, this is a crisp, sure play that shows Hollinger in command of his material.

Partly, that's because he is himself a violist with quartet experience. More important, he has developed as a playwright. But above all, "Opus" offers an absorbing 95 minutes of drama because it is so convincingly performed by its cast of five.

In this, the production doubly replicates its content. The essence of string quartets is a practiced, eventually almost otherworldly unity in which four instruments are played as if by one hand. The group develops an artistic soul.

Hollinger dramatizes this in his writing, with quartet members instinctively completing each other's sentences or communicating without speech, much as they complete their musical phrases. The second level is provided by the actors, who, having already performed in Philadelphia, take unity to a level at which they collaborate as seamlessly as the characters.

The story begins as the all-male Lazzara Quartet, which operates by a rigorous democracy, has just fired one of its members and is auditioning a young woman replacement. It proceeds both by flashback, revealing the tensions that led to the split, and forward through rehearsals to a command performance at the White House, at which it will play Beethoven's Opus 131, the one quartet not yet recorded for its all-Beethoven series.

I'm especially pleased that the play ends not with its plot lines tied up neatly, but with an explosion that opens new emotional vistas -- as though the quartet exists in real, continuing time.

The difficulty of seeming to make music is handled effectively by a recording by The Addison Quartet, with the actors miming play (bowing but not fingering).

The violinists, one obsessive, one warm but recessive, are played by Patrick McNulty and Greg Wood. David Whalen, a returning Point Park grad, plays the fired violist. We are more familiar with the delightful Erika Cuenca, playing his aptly named replacement, Grace, and Douglas Rees, as the cellist -- but Rees astonishes with the effortless depth of his performance.

Aside from the thinness of some characterizations, the only limitation is that "Opus" is basically another American play about relationships, our usual theatrical obsession. But it rises above that in the drama (both glorious and costly) of making art, exemplified in the staging.

So what will Hollinger have for us in 2011?