The start of the Oslo concert season always means a plethora of festivals popping up, from seemingly nowhere. With several festivals already well under way, and others a few days or weeks away, the Oslo Chamber Music Festival manages to assert its place as an important musical arena, with exciting musicians, well thought-out programmes and impressive music-making. Thursday’s opening concert offered an intriguing snapshot of the festival as a whole: an intriguing mix of known and unknown, old and new repertoire, all performed with the utmost conviction by all involved.

As the audience settled down, the pre-concert murmur was pierced by the scream of a girl gleefully running across the stage. First one, then another, then another. Two, three, all of them, screaming. What began as apparent joy became decidedly alarming. Girls running, screaming, first individually, then in unison. Maja Ratkje’s Ro-Uro (Rest-Unrest) was written for the Norwegian Girls’ Choir in 2007 and explores themes of war and peace, order and chaos. Ratkje draws on texts from the Nag Hammadi Library and Norwegian children’s songs, on light and movement, creating a piece of unsettling beauty. The end of the piece proved particularly disturbing. After layering several children songs on top of one another – again making the at first childishly innocent uncomfortable and claustrophobic – the singers turn their backs to the audience, shouting the names of dictators and despots past and present, corrupting the innocence of childhood with a world history of atrocities.

The Norwegian Girls’ Choir, led by conductor Anne Karin Sundal-Ask, gave an intensely committed and virtuosic performance of this challenging piece. It was made all the more impressive by the young age of the performers, ranging from six to sixteen. As Ro-Uro faded into silence, Schubert’s Du bist die Ruh filled the stunned silence. Mezzo-soprano Marianne Beate Kielland and pianist Håvard Gimse filled the piece with an uplifting tranquillity, restoring at least a semblance of order.

Kielland was then joined by cimbalom player Hans-Kristian Kjos Sørensen for a performance of excerpts from György Kurtág’s song cycle Hèt Dal, settings of short Hungarian poems. Gimse was joined by fellow pianist Leif Ove Andsnes for interspersed excerpts from Kurtág’s collection of piano miniatures Játékok. These little pieces by Kurtág showed a remarkable breadth of expression, each one containing its own little sound world, like the sensuous, verging on the seductive song Labirintus (Labyrinth) and the angular declamation of Ars Poetica, the cimbalom always lending the songs a quasi-folkloric sheen. Likewise, the piano pieces mirrored and commented on the songs, from the sharp angularity of the four-hand Harangok (Bells) to the ethereal glissandi of Örökmozgo (Perpetuum Mobile), played by Gimse alone. Gimse and Andsnes finished the first half of the concert with Schubert’s Fugue in E minor D952 for piano four-hands, gently undulating at first, the undulating relentlessly gaining purpose and direction throughout.

Andsnes returned after intermission for a performance of Beethoven’s Piano Sonata no. 18, Op.31 no. 3. Even though on the surface this piece can sound unusually cheery for Beethoven, Andsnes played it with a nervous energy, switching with ease between carefree elegance and anguished despair. His articulation was, as usual, remarkably crisp, every note clearly audible. The agitation of the second movement, with its legato right-hand melody over a bustling left-hand accompaniment, was filled with half-humorous aggression, ambiguous and uncertain of where to go, but going regardless. The third movement stood out as an oasis of grace and heart-melting simplicity, before Andsnes lunged straight into the fourth and final movement with manic energy, giving a serious edge to the easily overly jolly music.

The unease of the Beethoven metamorphosed into an uneasy, restless rendition of Schubert’s Fantasie in F minor, D940 for piano four-hands. Andsnes and Gimse took the melancholy, song-like opening rather faster than normal, just shy of having it sound rushed. This frantic quality continued throughout the piece, always whirling at is centre, until the final reprise of the opening melody, a little more assertive, a little less questioning.