Steven Isserlis / Wigmore Hall, London

Steven Isserlis is one of this month's flavours, and his short chamber music festival at the Wigmore Hall parades the company he keeps, including some distinguished performers. Wednesday's opening concert began - deceptively - in the manner of amiable music-making among friends, with Boccherini's anodyne String Quintet in F minor, Op 42 No 1. In its thumb-twiddling finale, violinists Joshua Bell and Daniel Phillips, viola- player Carla-Maria Rodrigues and cellists David Waterman and Isserlis, ended up with fixed smiles, as if to say, "Do believe us, we are having fun!"

The rest of the concert was on a more intense level. Olli Mustonen took the top and Stephen Hough the lower part in Schubert's sublime Fantasia in F minor for piano duet, so that the decorative aspect of Mustonen's action, arms flailing octopus-like, could be seen to advantage. His rather staccato attack and the players' sparing use of pedal minimised sustaining quality - already at risk because of Schubert's enthusiasm for the piano's highest and weakest register. Still, Mustonen shaded the plaintive opening theme nicely, and both players brought a lift to the central dance-like movement. Crucially, they hit on a convincing ratio of tempi from one movement to the next, so that it felt as if they had a common denominator; their balance and synchronisation were good, too.

Mustonen was the pianist in Messiaen's Quartet for the End of Time, and had no problem in sustaining a big, sumptuous sound. But it's the other three players who have the star solo turns here. I still haven't heard a cellist produce a nice sound in the fifth movement, and Isserlis's seemed a bit throttled. But clarinettist Michael Collins showed amazing control of tone and dynamics in the third movement, and, with Joshua Bell as violinist, the whole performance was not only very well prepared, it was also really fiery. If the elaborate recording rig meant a CD is on the way, it will be worth looking out for.

The novelty at Friday's concert was the premiere of Mustonen's Nonet for two string quartets and double-bass. About 16 minutes long, it opened just like a late Beethoven quartet, with a crescendo on a held note, leading to a slow, exploratory contrapuntal section followed by a vigorous Allegro. After enlarging on the opening gambit, the music then switched into the rustlings of nature and searching horizons of Mustonen's great compatriot, Sibelius, though Bell's brief exclamatory phrases recalled Janacek. The "Sibelius" music grew quite convincingly, before settling into an easier kind of busyness in a regular metre, and the whole work remained an unresolved assembly of influences.

n Series ends 7.30pm tomorrow. Booking: 0171-935 2141