Ducktastic Albery Theatre, London

Never mind that she's being treated like royalty - at her curtain call, for example, she emerges from an egg so spangled it looks to have been laid by Liberace. For the most part, this is a disgruntled luvvie duck, who scuttles across the stage sowing inscrutable mayhem and even develops a voice to complicate her subversiveness.

Daphne's mood, though, is only one of the difficulties facing Christophe Ursula Sassoon, the failed Las Vegas magician in Ducktastic, the Right Size's much-heralded follow-up show to their West End and Broadway smash hit, The Play What I Wrote.

If the latter was this double act's Chinese box-like tribute to Morecambe and Wise, the inspiration of the new piece is the perma-tanned illusionist duo, Siegfried and Roy, who worked with tigers until their career was curtailed by a public mauling.

The conceit is that Ducktastic is the show that Christophe (played with a radiantly fatuous messianic zeal by Hamish McColl) has mounted to try to woo back his wife-cum-stage-assistant whom he thinks is among the punters at the Albery.

To fill her place on stage, he recruits from the audience a nerdy pet shop owner from Portsmouth (Sean Foley) whose name, Roy Street, is elevated to Roy de la Rue. Concurrently, there's also a kind of show-within-a-show, involving the principals, a stage-struck usherette (Alex Kelly) and her bickering parents who are rudely propelled into the proceedings when, in one of several spectacular feats of illusion, Roy, dressed as sperm (don't ask), is fired from a cannon into their box.

Watching The Play What I Wrote, the audience had an affectionate familiarity with the source material and its conventions. And the show had genuine heart as it explored the troubled but touching interdependence in any double act between the funny man and the straight man.

But it's hard to know what precisely is being spoofed in the desperately inflated origins-of-life extravaganzas that make up the Ducktastic strand of the piece, replete with Al Pacino as the Voice of God. Likewise, there isn't a comparable, sentimentally satisfying, charge to the relationship between sorcerer and assistant. The wife makes only a couple of fleeting appearances; the magical master/servant reversals involving Roy and Siegfried (who winds up a hefty woman) feel flimsy because they have only just met.

I'm a total sucker for inspired silliness and non-stop, groan-worthy double entendres and barmily burgeoning plots. All the same, I have to register a certain disappointment with Ducktastic which, even under the shrewd direction of Kenneth Branagh, comes across as a concocted sequel rather than as a piece that has real spiritual affinities with the subject matter, as did The Play What I Wrote. It's not just the embarrassing failure of the climactic illusion at the press performance that leads me to describe the show as very hit-and-miss.