C-sharp minor — the mere words conjure up a sense of anxious edge, which is the feeling that drives "A Late Quartet." Starring Christopher Walken, Philip Seymour Hoffman, Catherine Keener and Mark Ivanir as the players, this is a chamber piece about chamber musicians that is set to Beethoven’s emotional Opus 131 string quartet — in C-sharp minor.

As much as the movie is shaped by the piece — Opus 131 is a complex, demanding work — "A Late Quartet" is not really about the music. Director Yaron Zilberman, a chamber music fan, is using the intimate collaboration required of a string quartet to examine the way in which lives become dangerously entangled over time. The nature of a quartet creates a closed and at times claustrophobic universe that often works in the filmmaker’s favor. But at times, it seems to constrain this exceptional acting ensemble, asked to play such a diverse and dissonant range of emotional notes.

The film, written by Zilberman and Seth Grossman, opens just as the Fugue String Quartet is about to begin its 25th season. Peter Mitchell (Walken), the group’s revered cellist, is dealing with the death of his wife and a Parkinson’s diagnosis that will end his playing. That cloud turns into a raging storm that threatens to not only divide the quartet, but destroy the very deep bonds between the musicians.

At risk is the long marriage between second violinist Robert Gelbart (Hoffman) and Juliette (Keener), known for her emotionally resonant viola. There are rising tensions as well between Robert and first violinist Daniel (Ivanir) when Robert dares to covet the first violin chair.

There is Juliette’s grief over Peter’s illness — he raised her as his daughter after her parents died — and the suggestion that Daniel might actually be the man she loves.

As if those weren’t complications enough, there is a budding relationship between Daniel and the Gelbarts’ beautiful and talented daughter Alexandra (Imogen Poots).

It is but one of the relationships in the film that is difficult to buy. The introduction of Robert’s running partner, a gorgeous flamenco dancer (Liraz Charhi), becomes a credulity-straining problem as well.

Hoffman, however, is completely invested in making you believe he is a world-class violinist, fitful in his second chair, and in that he is masterful as always. The strains in Robert and Juliette’s marriage feel real enough, never better expressed than in the sniping quarrel they have in the back of a taxi, a whispered exchange with words spit out like spoiled fruit. The overly polite sparring is priceless.

Despite all the upheaval and multiple stories, the script is spare.

The film is shot with a spareness as well, by director of photography Frederick Elmes, the lens lingering on the warm woods and exquisite lines of the instruments as often as the faces. The music itself is heart-wrenching, the esteemed Brentano String Quartet playing the Opus excerpts and the film’s composer, Angelo Badalamenti, creating a score that complements Beethoven in remarkable ways.

But Zilberman’s minimalistic approach fits the idea of the film better than it fits the actual film. It leaves this melancholy mood piece with some beautiful moments, but unlike Beethoven’s work, "A Late Quartet" ultimately feels unfinished.