Simon Holt and the Nash Ensemble go back a long way. One of his first commissions was a piece for the group in 1983, and the premiere in the Nash's morning concert at Cheltenham, where it was sandwiched between Shostakovich's Seventh String Quartet and Grieg's solitary quartet, was the seventh work Holt has written for its players. Unlike its vividly scored predecessors, though, the new piece, 4 Quarters, is composed for just a string trio, an instrumental combination that Holt described in a short introduction to the performance as among the hardest there is for a composer to master.

As the title suggests, each of the four movements is named after something that belongs in a set of four - there's a humour (choler), a point of the compass (north), a season (spring), and a classical element (ether). The immensely challenging trio-writing seems to carry on where Holt left off in his violin concerto Witness to a Snow Miracle, first performed earlier this year, as if the success of that wonderful piece emboldened him to push further at the limits of what string players can achieve.

So the first movement is a coruscating viola solo, authentically choleric and delivered with maximum intensity by Laurence Power. The second is a glacial study in textures, with Paul Watkins's cello singing out above his colleagues. And the third is full of rapturous solos for violinist Marianne Thorsen, which regularly burst into life. The last movement is the most elusive and the most intensely personal, with delicate thematic shards floating in space until they are brought up short by fierce fortissimo chords. Like the whole work, it's beautifully achieved, profoundly individual and ultimately enigmatic.