The xx @ secret space, Manchester International Festival, 6 Jul

She breathes; we breathe. The quick sting of her plectrum against steel – it reaches us before its amplified echo finds its way out of the speakers. Lit from beneath, The xx's Romy Madley Croft carefully treads a square of glowing, translucent floor that's thick like ice, reinforced with a criss-cross of metal braces. Sixty people, assembled around its perimeter, track her with a uniform gaze – equal parts disbelieving and transfixed – as she and bandmate Oliver Sim circle each other in a languid game of cat and mouse. Their chemistry is an alarming, arresting force; they court and joust almost in reverse, lying in wait, retreating in deference.

This is the second of 18 in-the-round performances that bring a new meaning to the idea of the 'intimate' gig, and make for perhaps the most impressive feat – in terms of execution of artistic vision – that Manchester International Festival has realised in its four biennial instalments since 2007 (Adam Curtis and Punchdrunk's immersive theatre nightmare It Felt Like a Kiss, from 2009, runs a close second, though that was a visceral experience for entirely different reasons). As the purposely constructed space – a soft enclosure curtained by billowing white sheets – begins to expand, contract and shape-shift during a delicate lightshow that manipulates audience members' spatial awareness, the full extent of the imagination behind this 'in residence' show is revealed. When the fabric falls at the juddering climax of a tectonically bass-heavy Shelter, and when measured, throbbing strobes reach out into the darkness beyond like searchlights, we understand we're in an altogether other environment – a vast cavity, in fact; the foundations of Chetham's School of Music.

Suddenly, there's a chill; the band slow to a halt, like wind-up figurines out of potential. As we exit the way we entered – through fusty, mouldering emergency access tunnels beneath Victoria train station – most are beaming, speechless; others tremble. Blink – and you dreamed it.