If the aim of Sonica festival is to place image and sound on an equal footing, then opera, a hybrid of music and theatre, is certainly one way to fulfil that. Artist and composer Mathis Nitschke’s Viola is the only opera in the Sonica programme, but it’s unique in more than just that. Set in St. Enoch shopping centre, the audience sit inside an empty unit, and watch the real life scene of shoppers going about their business. We focus our attention on Martina Koppelstetter, the sole “performer” of this act. As she sings, her voice is transmitted to the audience via the specially-rigged glass windows, and mixed live with pre-recorded orchestral accompaniment by Nitschke, who sits behind us at the back.

This isn’t the first time Viola has been performed. It debuted in Munich in 2005, but today’s version is (mercifully for me) mostly in English. It works well in the shopping centre, with the character Viola’s alienated and confused song – performed with aplomb – contrasting with the groups of families and kids doing some Saturday shopping. She gestures and paces, but shoppers awkwardly ignore her. She is trying to make a connection, but she can’t. However we the audience are noticed by most people who pass. We start to wonder who the spectacle is here – the woman singing randomly in public, or the people sitting in a shop window staring at passers by.

At one point, Koppelstetter breaks the fourth wall as she comes right up to the glass and addresses us. She even desperately propositions one of us. It’s uncomfortable and affronting – in a good way. The tension piques. This moment is brief though, as is the rest of the opera, lasting only 20 minutes. As Viola wanders into Debenhams and the music fades out, we are left not sure if it’s finished. It doesn’t feel like enough.

Why has Nitschke created this hysterical woman? This song functions as an aria, and that would normally come in the middle of an opera. Maybe it is important for operas to have sections and multiple characters. The set up is very effective and this is an enjoyable watch, but without elaboration on Viola’s story, motivations or relationships, it rings a bit hollow.