The Great Downhill Journey of Little Tommy (Summerhall, Edinburgh)

Theatre as gig or gig as theatre? There's a subtle difference, I think – something to do with whether we're free to drink and dance, perhaps, or just asked to watch. Either way, the form's been on the rise for a while: last year's KlangHAUS put a punk band in an old animal hospital; nabakov's Symphony was written especially for the Latitude Festival. Let It Be is basically a tribute band in the West End, right?

Jonas Vermeleun and Boris Van Severin might be theatre's McFly – though they'll likely gag at the label. Heartthrob handsome and swaggeringly charismatic, the two Belgians front up a band dressed all in black and they've set more young hearts aflutter this Fringe than most of us ever will. Vermeleun, teeny and buzzing, takes vocals and keys; the brooding Van Severin's on guitar. Both are powersurge performers, completely unselfconscious and completely dazzling.

Little Tommy is a concept album of a show: a string of songs that follow a squeaky, young kid who leaves his hilltop home and strolls to the sea, meeting strangers en route. Each encounter gets its own musical style: his mother squawks to screeching rock, muscle-bound workmen get an industrial beat, partyboys fill the room with funk. Vermeleun stumbles around as a woozy alocoholic; Van Severin trills as a teary cougar. Behind them, a scroll of his journey is painted live, full of surreal dreamy details: cracked eggs with faces and cock-and-ball soldiers.

At the end of the day, or at the bottom of the hill, it's a twee little parable about picking your path in life and the question Tommy's left with is where he belongs. Mostly, though, it's so much fantasia – all fizz, not much substance – but played this vivaciously, it goes straight to your head.

The Great Downhill Journey of Little Tommy continues at Summerhall until 30 August