Nathan The Wise, Hampstead Theatre, London

Lessing's drama is rarely encountered on stage. But, as the dangers of religious fundamentalism escalate, it has finally made the leap from cobwebbed classic to vital play-for-today. The kudos for rediscovery goes to Steven Pimlott, who two years ago directed an acclaimed revival at Chichester. Now London gets the chance to see the piece in Anthony Clark's production, which uses the same fresh and witty prose translation by Edward Kemp.

The action is set in 12th-century Jerusalem during the Third Crusade, with the Jews caught between the Muslim forces of Saladin and Christianity's own Jihadists. The merchant, Nathan (twinkling, stoical Michael Pennington), arrives back from a business trip to discover that his daughter has fallen in love with a truculent young Knight Templar (Sam Troughton) who rescued her from a fire. The girl owes her life to a man whose life has also been saved by a twist that seems to come from the world of romance, for the Saladin has spared the Templar because of the youth's resemblance to his dead brother. The play shows Nathan using all his humanity to mediate between these men. Love may get the better of the Templar's prejudices, but bigotry resurfaces when he hears that the daughter was born a Christian and placed in Nathan's care as a baby.

The crucial scene is the one where the Jew is compelled to adjudicate on which religion represents the true faith. He answers in the form of a parable about a father who, liking his three sons equally, had two identical copies made of his ring so that they can all inherit it. Which, though, is the original? The story demonstrates that it's the force of one's humanity, rather than the stripe of one's faith, that matters.

There are some fine performances - Michael Pennington excellently suggests a man who has survived terrible personal loss without it souring his soul; Shelley King exudes droll cunning as the Saladin's sister. But the progress towards the romance-like close is enervatingly sluggish.

To 15 October (020-7722 9301)