There are some transcendent moments of silliness in The Trap’s over-the-top return to the Fringe, even if the joke runs dry before the show reaches the final overture.

Picking up where their Bad Play trilogy left off seven long years ago, this talented, energetic trio have now fixed their targets on the world of musical theatre – even though the genre doesn’t take itself so seriously as heavyweight dramas, automatically reducing the impact.

But musicals do have a well-defined set of conventions, which are duly trampled under their soft-shoe shuffle. Add into the mix of malfunctioning props, forgotten lines and botched musical cues – and the result is a frantic carnival of the inept, keeping the spirit of Acorn Antiques alive.

Dan Mersh plays Johnny Everyman, who dreams of one day escaping from his overbearing parents in the tiny village of Little Smallton. Indeed, he makes the trip to the Big Smoke of London/Edinburgh (they haven’t quite decided) to make his fortune, learn about the transport system from lyrical mobsters, and become Prime Minister. Though even for a deliberately bad musical, the plot twist involving alien abduction, seems a leap too far.

But the chaos is always entertaining to watch, and occasionally hilarious, especially as the players start silently blaming each other, the techie and the prompt girl for the failings that pile up in this car crash of light entertainment. And a pyrotechnic effect that doesn’t fire early on adds the frisson of an unexploded firework to the whole musical.

The songs themselves tend to be played fairly straight – parodies of the genre rather than badly sung. These include the opening number Life Is A Musical, nicely setting the scene, and a jaunty ditty extolling the virtues of the BNP – cheeky rather than the outright glorious offence of Jerry Springer: The Opera’s choreographed Klansmen or the high-kicking Nazis of The Producers.

Elsewhere, an interminable scene-stealing song in which Paul Litchfield’s sandwich-shop owner laments his lot demonstrates that his favourite filling matches his acting style: ham. Jeremy Limb, always the musical backbone of the trio, delivers the songs he leads more in the over-enthusiastic spirit of real West End productions, letting the ridiculous lyrics do their work.

They’ve allegedly cut several hours out of this to fit the Edinburgh hour – and the truth is another 15 minutes wouldn’t be missed. But there’s more than enough exuberant, unpredictable silliness for this welcome Edinburgh return to be well worth a look.