Long live this mad monarch

I have seen Henry IV, Luigi Pirandello's classic 20th century drama of madness and masks, strong illusion and infirm reality, in a disturbing new light, thanks to Ian McDiarmid's extraordinary title role performance.

The monarch in question does not precisely exist. His identity has been seized by an Italian nobleman, who since falling from his horse 20 years earlier has believed himself to be the medieval German emperor, Henry IV.

Attendants assist him in maintaining this false identity. Then one day the countess he loved when young, comes calling in the attractive shape of Francesca Annis, accompanied by her daughter, a jaded sophisticate of a lover (amusing David Yelland) and Robert Demeger's psychiatrist who has a cure for the king in mind.

Rex Harrison and Richard Harris, who played the fantasy monarch in the only major London productions since the British premiere 80 years ago, embedded their large, idiosyncratic personalities in the role.

In their wildly different ways they made Henry a grand period piece, a starry example of well-born madness. McDiarmid, in Michael Grandage's atmospheric, moderndress production and Tom Stoppard's fluent, contemporary version of the play with its occasional misbegotten crudities, is rivetingly different.

Here, on Christopher Oram's imposing set of lofty columns and stone floors, with the smart visitors all dolled up in contemporary Versace togs, is a Henry IV for today, that removes the glamour and grandeur from the kingly role-play.

McDiarmid totters on at geriatric pace, dressed in just a sack-cloth, cheeks stained with red make-up or blood, his hair as wild as a night in one of Soho's lowest dives.

He does not so much look like a man madly playing a king, as one of Samuel Beckett's crumbling, crumpled relics, almost on their last legs.

When he speaks his voice is pitched at the level of an anguished, occasionally unintelligible murmur. The key to McDiarmid's performance is the line: "My life has been one humiliation after another." His suitably desolate Henry has passed beyond the mad game of pretending to be a king and become an enfeebled old man before his time. Madness has him in a strangling grip.

This impression, true to Pirandello's relish for the volte-face, turns out to be false or misleading. With Annis's languidly narcissistic countess he speaks of his determination to cling to the illusion of youth by dyeing his hair and the cruelty of time that fritters life away without your noticing.