London Baroque, St John's, Smith Square, London

François Couperin's Leçons de ténèbres pour le Mercredi Saint (c1714) surely remain among the most poignant pieces ever inspired by the liturgy for Holy Week. The first three of a sequence of nine (the remaining six, alas, have never turned up), these set some of the most desolate verses from The Lamentations of Jeremiah, for one or two high voices and continuo, in long, fine-spun lines, at once gently anguished and radiantly serene, and of almost unearthly beauty.

In this concert, by those seasoned early-music sopranos Emma Kirkby and Agnès Mellon and the four period players of London Baroque, as part of the Lufthansa Festival of Baroque Music, the Leçons proved the triple pillars of a singularly satisfying programme. After a short prologue comprising several sprightly Trios pour le coucher du Roi by Lully, Kirkby and Mellon respectively undertook the first and second Leçons, separated by Couperin's entrancing suite, Le Parnasse, ou l'Apothéose de Corelli.

Neither soprano started at their inimitable best. It wasn't always so easy to distinguish between Kirkby's execution of Couperin's delicate ornaments and a slight flutter in her tone, while Mellon's fruity lower register was under less than perfect control. But experience and skill soon reasserted themselves (and the pieces made their usual mesmeric impact).

Meanwhile, London Baroque's stylish viola da gamba player, Charles Medlam, further enlivened the Franco-Italian mix of Le Parnasse by reading out Couperin's picturesque descriptions of Corelli's reception by the Muses, his deification by Apollo, etc.

The second half opened with a pair of duet items: Purcell's late Latin elegy on the death of Queen Mary, O dive custos, full of his most jagged melodic turns and searching chromaticism; and Couperin's festive little Regina coeli laetere. Then we had Sonata no 10 in D major from Purcell's Sonatas in Four Parts, its cut and thrust brightly brought off by the violins of Ingrid Seifert and Richard Gwilt, with Terence Charlston on sparkling harpsichord.

And so to the sublime third Leçon, with the two sopranos interweaving their way through the undulating duets with which Couperin sets the initial Hebrew letter of each of his verses in a chaste ecstasy of sound. The final appeal to return to the faith, "Jerusalem, convertere ad Dominum Deum tuum", could hardly have come over more plangently in its restrained elevation.