Although not one of the four commissioners, The Royal Opera is to be congratulated for giving the UK premiere of George Benjamin's Written on Skin so soon after the first staging at last year's Aix-en-Provence festival.

It's a triumph, a dark and disturbing opera. With the help of three angels we are taken back to the twelfth century for a medieval story involving The Protector (a landowner) - he owns everything and everyone - including his wife, Agnès. She falls for The Boy who is commissioned to celebrate The Protector's achievements in the form of an illuminated manuscript. Her unfaithfulness is severely punished; The Boy is murdered and his heart cut out, cooked, and served up to Agnès, literally on a plate. It makes for 90 minutes of sexual and dramatic tension.

Musically, Benjamin's typically painstakingly notated score both complements and develops the action and is also persuasive on its own term, a slow-burn that never sags, although taking a break between the three scenes for minimal changes to the furniture does lose a little atmosphere: one wishes that Benjamin could compose orchestral interludes to cover these hiatuses. That said the invention is focussed and revealing enough to effortlessly pick up where it left off and Benjamin's orchestration is typically fastidious and subtle and includes the beguiling sounds of bass viol, glass harmonica and mandolin, catching the ear with clarity and very particular colour.

The psychological perspectives of the story are illuminated by the orchestra, excellently played, conducted by Benjamin himself with authority. There isn't much fast music, and few climaxes, but the latter are searing and there is plenty of meaningful activity emerging from the pit. In many ways, while remaining true to himself, Benjamin is sometimes found in Birtwistlian territory, and that is a plus.

Martin Crimp's text is generally good, with perhaps a doubt about the characters reiterating lines that concern themselves, a running commentary. Katie Mitchell's direction, superbly lit by Jon Clark, while without excess, might be thought a little distracting at times for this ancient and modern set - centuries-old for the story and 21st century for the office compartments manned by actors sometimes moving in slow-motion, as the main characters come and go between the time zones.

A super cast of five singers include Christopher Purves's Protector, dictatorial and unforgiving, the countertenor Bejun Mehta's Boy, innocent but inquisitive, and Barbara Hannigan's enigmatic if eager Agnès; as ever, this wonderful devotee of new music is fearless as singer and actress. Victoria Simmonds (the only performer not in the Aix production) plays Agnès's sister and Allan Clayton is her husband John.

Written on Skin is not only at Covent Garden, it is being broadcast on BBC Radio on 3 June, is now on CD from Nimbus (beautifully recorded by Radio France) and is due on DVD from Opus Arte ere long. But seeing this opera live is to be involved to the fullest with an impressive coming-together of words, music and theatre.