Who would have thought that Shostakovich's centenary celebrations at the Barbican would produce music we have never heard before? The composer's second film score, to Odna, dates from 1930 - a turning of the gyre from the raw energy of Shostakovich's springtime and engagement with constructivist and avant-garde movements in Leningrad, to a still veiled critique of the nascent Stalinist tyranny.

The ingenious, epic footage from Lenfilm studio is, accordingly, part propaganda, part subtle subversion, for which it was withdrawn after a short run, and unearthed only a few years ago. A beautiful young woman leaves her sweetheart and native city of Leningrad to teach shepherd children and expose corruption in the desolate Altai mountains, surviving a scurvy plot to freeze her to death through courage, the peoples' love and benevolence of higher socialist authority.

Shostakovich's score existed only in parts: British conductor Mark Fitz-Gerald, in collaboration with Shostakovich's widow Irena faced a daunting task of editing and reconstruction. The music bursts with ideas and textural experimentation that characterise Shostakovich's early period: there is a barrel organ (adapted for what sounded like a throaty harmonium) and a part for a Mongolian throat singer.

But above all, we hear, at an early stage, Shostakovich's deployment of what would become one of his sharpest weapons: irony. Epic narrative moments are accompanied not only by symphonic climaxes but also dissonances, quirkiness and even mild suggestions of the grotesque. It is not only the heroine, one feels, who is isolated.

Fitz-Gerald's commitment to both score and event brought the best from an orchestra playing in the wake of the LSO's shattering account of the Fourth Symphony with Gergiev only a few days before - a terrifying reminder of where tonight's still buoyant music by the youthful composer would lead, as tyranny escalated into terror.