First Night: La Bête, Comedy Theatre, London

Travels with Molière and a monologue masterclass

"La Bête" is a "beast" and a "fool" in French, and it's one of the puzzles in Matthew Warchus's colourfully inflated, Broadway-bound revival of this 1992, 17th-century oddity that you never really know to whom the title refers: the actor, the writer or the patron.

These are the three protagonists in a stylish, one-off rhyming text by the American playwright David Hirson, and they are played at the Comedy by Mark Rylance, David Hyde Pierce and Joanna Lumley; casting with the feel of covering all bases demanded by some critical Polonius: respectable classical, comical sit-com musical and cut-glass posh national treasure.

For about one hour of its length, the show is enjoyable because it's so intriguing. A magnificently lit banquet is in progress on the Languedoc estate of the princess. The stage then literally deliquesces in Mark Thompson's design into a grand library where battle is joined between the favoured playwright, Elomire (ie Molière) and the upstart vaudevillian Valère, played with Ken Dodd comedy teeth by Mark Rylance, spitting on every line and chomping on his own integrity.

I saw the British premiere directed by Richard Jones, with Alan Cumming playing this bolshie new actor, and have an idea that the whole thing is about Molière's vagabond company, including the Béjart family, touring the southern provinces in 1654, several years before the Parisian glory days at the Palais Royal. But I'm stymied, now, as to what it all really means.

None of the issues in the "comic war" debate and Molière's famous preface to Tartuffe come across, nor are they meant to. So, what is Hirson actually proposing? An argument about the theatre, the conflict between intellectual and commercial imperatives, and an age-old bust-up between old and new orders in showbusiness?

It should be more than enough, but the play runs badly out of steam in the last 45 minutes, which seem to go on forever. This is where Joanna Lumley's princess – a role rewritten, to no great effect, from the masculine, preening arts-loving aristocratic booby of the original – supervises a command performance of Valère's parable of the Two Boys of Cadiz, and Hyde Pierce's slow-burning Elomire is left to contemplate the beast within his rising comic muse.

Rhyming couplets have to be exceptionally good to sustain a whole evening and we now see that Hirson's are not in the Tony Harrison class of Molière adaptations, nor even the Richard Gilman. But Rylance makes a virtuoso triumph of his uninterrupted 40-minute monologue (Cumming came in at just 25 minutes; he was more tumultuous), despite the lack of stage vivacity around him.

The Russian dramatist Mikhail Bulghakov, in his Molière play, pitted the successful dramatist against his sponsoring monarch, whereas Hirson flirts with history in his artistic stand-off and suffers by not being specific enough. Elomire is in trouble with the prince, but you get no sense in the production of a serious dispute. Ms Lumley is gorgeous and beautifully coiffed and dressed, but you don't know, really, where she's coming from.

At a time when good new plays like Jerusalem and Enron have made serious inroads in the West End, I was expecting, and hoping, that La Bête would have elucidated the shock of the new in the land of the dinosaurs, but it hasn't worked out like that.

Hyde Pierce's banked-down acting is a subtle delight, and Rylance proves yet again his astonishing, protean versatility. But his Valère is a feeble follow-up to his shape-shifting Johnny Rooster in Jerusalem in a play that promises much more than it delivers and ends up curling into a cul-de-sac of self-referential platitudes.

To 4 September; 0844 871 7622; www.labetetheplay.com