The last of the six quartets Mozart dedicated to Haydn, K. 465 is officially in the sunny key of C major, but it owes its "Dissonant" nickname to its slow, tense introduction, full of unresolved harmonies over a throbbing cello line. Soon enough, this disorienting Adagio gives way to the first movement's bright, Allegro main matter. The first violin sings out the short-phrased principal theme, which the other instruments soon pick up in contrapuntal imitation. A second, more jittery melody and a third in triplets all become fodder for a brief development section, although it's the first theme, now with a minor cast, that dominates the proceedings until the recapitulation soothes the troubled quartet—the exposition returning, of course, without the baggage of the "dissonant" introduction.

The second movement, Andante cantabile, wraps itself in warm F major, with all four instruments exploring a variety of highly lyrical thematic passages. Third comes a witty, Haydn-esque Minuet (and one that would influence Beethoven), full of sudden dynamic contrasts and pitting various combinations of instruments against each other. The brief Trio section dips into C minor for an episode of agitated pathos. As it begins, the finale (Allegro) has every indication of being a conventional if quick rondo, but the music continually veers into unexpected harmonic territory, skidding into the minor and fragmenting the themes; this is perhaps a sonata-allegro movement, with the development section split among the episodes of a rondo. Performers may play this as either comedy or drama, but the music is really a bold melding of the two.

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