Betwixt! Trafalgar Studio 2, London

There are boy-meets-girl and boy-meets-boy musicals. It is a fairly safe bet, though, that this is the first boy-meets-disembodied-head-with-Bavarian-accent tuner. Will it set off a trend? The love between this unlikely couple is at the centre of an endearingly daft and reprehensibly enjoyable show, written and directed by Ian McFarlane.

How did our lovebirds meet? The leading character, Bailey (a lank, likeable Benedict Salter) is a blocked writer in New York. With his new gay flatmate, Cooper, all physical campery and tartly timed gabbiness in Steven Webb's very funny performance), he is plunged via a strange doorway into a parallel universe, to fulfil a prophecy that a brave hero and a great queen will come to the rescue.

Evil spirits swap people from this world with their counterparts in ours. Hence the hunt for a washed-up TV soap star who has been substituted for a prince (two of three roles gamely essayed by the former Blue Peter presenter Peter Duncan). Another triple is notched up by Ellen Greene. By turns ickle-girl ditsy and drag-queen sultry, she's a tongue-in-cheek fusion of her renowned Audrey from Little Shop of Horrors and our own Fenella Fielding as the Princess, the Enchantress and, best of all, a siren Nymph who is affronted when Bailey resists her charms ("Look at me and tell me you don't want to French me") in favour of Miranda, his beloved head.

Her daisy-decorated bonce poking out of a trunk, Ashleigh Grey is one hilariously firm and bad-tempered top-end of rural Teuton in this role. She is also in terrific voice. "A Strange Sort of Love Song", in which she is pulled around by her beau in a loopy Latin American dance, is one of the highlights of a show that boasts a versatile chorus (who impersonate everything from gyrating nymphs to tap-dancing paparazzi) and a score that ranges between perky pastiche and (more questionable) tear-stained uplift.

The story is bonkers and the moral unearned – why are we always being enjoined to "see through the eyes of a child" by musical writers, most of whom have all the childlike innocence of a well-thumbed copy of Variety? But the show bursts with infectious zest in this little theatre and you emerge with a stupid grin plastered over your face.

To 10 September (0844 871 7627)