In 1790s France, a young noblewoman, Blanche de La Force, decides to enter a Carmelite convent. As the increasingly paranoid revolutionaries close in, Blanche, her family and the nuns hold a series of discussions on their circumstances, the danger, their faith and, ultimately, their martyrdom. You might think that it doesn't sound much like exciting material for a dynamic, dramatic opera - but you'd be wrong. Poulenc's music and the dialogue he adapted from Georges Bernanos's play provide all the power and drama you might ever wish for, and the Guildhall School's opera department delivered it with authority.

To enjoy Dialogues des Carmélites, there are a couple of things you have to accept. The first is that it's pretty static. The entire piece is a series of tableaux as various combinations of characters come on stage to discuss the issue of the moment. Within each scene, this production has very little movement. Maybe some director will come up with a way of adding some in without wrecking the piece, but I find it hard to imagine how. The second is that the whole work is underpinned by Christian principles, which you have to accept as a premise.

If you're fine with those two aspects, what you're watching is a masterpiece. Anna Patalong gave us an intense study of Blanche's character: she is the person who spends her entire life being told what to do by the people around her - family, the mother superior, the revolutionary authorities, even her former servants. Only at the end, for the first time, does she take an action that is totally of her own volition. Cátia Moreso gave us a truly terrifying performance as the old Prioress who loses her faith in the face of the extreme pain from her terminal illness. Sylvie Bedouelle was vocally superb and dramatically convincing as Mère Marie, the strongest-willed of the younger nuns, Sophie Junker sounded beautiful as the light-hearted Constance and Charlie Mellor looks like a heldentenor in the making, delivering huge firepower as Blanche's brother, frightened by everything he sees around him.

Poulenc's music is breathtaking. To my ears, it's a kind of post-impressionist style, bearing the same relationship to impressionism as Cézanne or Van Gogh's paintings do to those of Monet and Degas. Poulenc's music is clearly from the same family as Ravel and Debussy, but the colours are brighter, the contrasts harsher and the overall experience far more intense. Time after time, I was knocked for six by an interwoven melodic phrase or some subtle piece of harmony, and the Act II settings of the Ave Maria and the Ave verum corpus are exquisite.

For the most part, conductor Clive Timms did a fine job of bringing the music to life. One of the mixed blessings of productions at the major conservatoires is that everyone in the orchestra is an aspiring soloist, so you get some fantastically talented playing, accompanied by the occasional moment where it all goes a bit haywire. The acoustics in the Guildhall's Silk Street theatre don't help: it has harsh, reverberant surfaces and a very deep orchestra pit which gives something of a foghorn effect. My other problem with the performance was in the French accents. Apart from the native French speakers, I suspect that most of the cast sing a lot more Italian, and they come out sounding like a bunch of Marseillais gangsters. If you don't speak French, it won't bother you, and, to be fair, I usually get the same problem with French opera at Covent Garden.

But all in all, this was a fine exhibition of the talents of the Guildhall students (and with Elaine Padmore, the Royal Opera's Director of Opera, in the audience for Act I, they can't have hoped for a better showcase). It's the third student opera I've seen this year, and it proves yet again what fantastic value for money these performances provide. But most of all, this production of Dialogues des Carmélites was also a fine advertisement for the bite and intensity that 20th century opera can bring.