The Malcontent, Gielgud Theatre, London

Shakespeare, of course, has an influence on contemporary playwrights, contemporary language and contemporary thought. But what is examined far less is the influence he must have had on his own contemporaries and the dramatists who followed him. The fascinating season of rarely performed plays by Shakespeare's contemporaries and successors, currently being staged by the RSC in London, shows just how massive that influence was.

The background to this season has itself been a drama. The RSC's financial problems and departure from its Barbican home meant it was not going to be able to transfer the season to London, despite an unexpectedly sold-out run at the Swan in Stratford. The 28-actor ensemble appealed to the West End producer Thelma Holt, who approached fellow impresario Bill Kenwright, and they agreed to bring it to the capital.

I suspect there has never been such a bold experiment in the heart of London's theatreland as putting on five plays that few Londoners, and frankly few avid theatregoers, would recognise. But, to judge from the first offering in the season, John Marston's The Malcontent, it was a risk well worth taking.

In this 1603 Jacobean tragicomedy, a deposed Italian duke returns to his court disguised as the malcontent of the title, and both comments upon and encourages its lust and corruption. The director Dominic Cooke transposes the action to a 1970s Latin American military dictatorship, a leap that works surprisingly well. Antony Sher's Malevole, a greasy-haired, vicious schemer, a cross between Iago and Uriah Heep, is a wonderful spectacle. He looks so seedy you feel you can smell him from the stalls.

But while Sher dominates the stage, he does not possess it. This ensemble is a first-rate company in which Joe Dixon as the narcissistic, cigar chomping dictator, Mendoza, and Amanda Drew's sulky, sexually volatile duchess also stand out.

For all the genuine delight of discovery in a rarely performed play, Marston is Marston and Shakespeare is Shakespeare. Most notably, the language of Shakespeare transcends that of Marston, whose imagery is less poetic and whose verse is less affecting. When Sher's malcontent dwells on his inability to sleep, the speech has a sense of irritation rather than the anguished soul-searching of Henry IV's famous soliloquy. Marston's characters, too, do not always strike us as real beings whose fate we care about.

That the evening is compelling and often extremely funny is largely down to Dominic Cooke's spirited direction. The stage and costumes are a blaze of colour, and he brings out every iota of the play's sex and slapstick to make this an intriguing and rewarding discovery.

To 25 January (020-7494 5065)