Smash, Menier Chocolate Factory, London

In these days of non-stop cross-disciplinary adaptation, here's a genuine first: a stage play about the making of a flop musical based on a television drama that is actually a coded analysis of the flop musical's creative team – who are producing another musical altogether in the current performance without songs.

Smash! is interesting on three counts: it's the late, great Jack Rosenthal's only stage play – it premiered at Watford in 1981, starring his wife Maureen Lipman, but never reached the West End; it pairs the ever urbane and distinctive Tom Conti as a thickly accented Jewish producer with dapper Richard Schiff, aka Toby Ziegler of The West Wing, as a big-time Broadway composer; and it breathes fairly funny new life into that old dinosaur of "putting on a show".

So, from moment to moment, it's reasonably diverting. But Tamara Harvey's production does little to flesh out thinly written characters or sort out the structural shabbiness of a script (with additional material by Rosenthal's daughter, Amy) that hobbles awkwardly between hotel bedrooms in New York, Manchester and London.

The whole thing is a good-humoured exercise in bitterness recollected in tranquillity. Rosenthal's television play Bar Mitzvah Boy was re-written as a 1978 flop musical of the same name with music by Jule Styne (who wrote Gypsy and Funny Girl) and lyrics by Don Black.

Conti plays a copy of Bar Miztvah Boy's producer, Peter Witt, a successful agent who made up for his lack of theatrical nous with old school charm. Conti does all this with a patient shrug and an affable twinkle. He's far less annoying these days, and no longer keeps running his right hand through his luxuriant (now greying) mane.

But there's something forced about the crisis surrounding the new show, as if the characters are playing dumb to create it. Natalie Walter, for instance, as Liz, the novelist from Wimbledon whose script is a stumbling block for the composer on principle (he's never heard of her, he's written 28 Broadway shows etc), is strangely unconvincing as a lost soul.

To 8 May (020 7907 7060)