Clemency, Royal Opera House, London

Less is more: in James MacMillan's music, every note counts. And never more so than in Clemency, the Scottish composer's brand-new chamber opera, which packs questions powerful, emotional, philosophical and religious into just 45 minutes. With his regular librettist Michael Symmons Roberts and the director Katie Mitchell, MacMillan has created a terrifically intense, focused and inspired musical work on a thought-provoking parable, updated to the present day.

Sarah and Abraham, a dowdy middle-aged couple in a run-down apartment, offer hospitality to three men apparently in need of shelter. But the strangers are angels: they bring a divine message that Sarah, despite her age, will soon bear a son. Then, though, they change into suits, concealing guns. Their mission is to take revenge on two towns that have treated outsiders with cruelty. Abraham argues for clemency. The ethics of "collective punishment" are never far away.

Mitchell's staging and the excellent designs by Alex Eales present this fable in a tripartite frame that suggests an altarpiece, while remaining naturalistic behind it. First, for several music-less minutes, Sarah cooks, birds sing, planes pass overhead. Abraham, alone at prayer, sings long phrases with quasi-Middle Eastern ornamentation. But the characterisation is unfailing: Sarah, sung by the marvellous Janis Kelly, has soaring, palpitating and plunging lines as her emotions are buffeted by fear and elation. Abraham, the full-toned Grant Doyle, is straightforward, humble but tenacious. The "triplets" are heard first in close harmony, almost as if with one voice at three pitches: an otherworldly sound, performed with frightening power by Adam Green, Eamonn Mulhall and Andrew Tortise.

But there's another character: the orchestra – the strings of the Britten Sinfonia, conducted by Clark Rundell. They play as if possessed in instrumental episodes that seem to argue the points, amplify the emotions and ratchet up the tension. These passages structure the score just as the three-part picture-frame structures the staging.

The end, though, seemed rather abrupt. In the ensuing long silence, we waited and hoped for a few extra concluding minutes.

To 14 May (020 7304 4000)