At the Edinburgh festival, an extraordinary show lays bare the enormity of grief | Brian Logan

When someone you love dies, the grief can be almost unbearable, but there can also be a sense of something valuable in the mix – as if a veil has been yanked back so you can momentarily see life, and what matters about it, clearly. When I’ve had those experiences, I remember thinking: “Please let me hold on to this insight, if or when the grief fades.” But you never do: daily life, and its less profound priorities, take over again at the wheel.

This then is some of the value of a new show by the always extraordinary Sh!t Theatre , entitled Or What’s Left of Us: it pulls the veil back again. Becca Biscuit and Louise Mothersole have both experienced grievous loss – of a parent in Mothersole’s case, and of a partner in Biscuit’s: Adam Brace, who was also the duo’s director, before he shockingly died last year . The show finds them uncertain, in light of that, whether they can even be Sh!t Theatre any more. So out go their usual white-painted faces, the video material, the alt.documentary zeal – and in comes total absorption in folk music, as a lens through which to consider death and bereavement, as generation upon generation have had to live with it (because what alternative is there?) before.

Full disclosure: I know Sh!t Theatre and knew Brace, mainly through my work at Camden People’s theatre . Even if I didn’t, mind you, I wouldn’t want to attach anything like a star-rating to this show, which would feel awfully dissonant. For four-fifths of its duration, Or What’s Left of Us is characterised by Biscuit and Mothersole’s usual brisk humour, boozy bonhomie and gorgeous harmonies. They wear Wicker Man-like headgear and pass around a bowl of beer. They join the community at a well-loved Yorkshire folk club (only for that club to be destroyed in an arson attack). They go on a mushroom binge at a music festival and schmooze Steeleye Span.

That’s the show’s melody, which supplies delight without ever concealing the low drumbeat of anguish beneath. “Are you alright?” they pause to ask one another. “No,” they reply.

Only in its closing stages does the show zero in unflinchingly on the enormity and unfathomability of grief (“sometimes there are no answers”), as the pair lay out with breathtaking starkness their experiences – step by step, image by image, ache after ache – of appalling personal loss.

It sent me and a friend back out into the world stirred into a recollection of our own bereavements and stunned, really, into wordlessness. Which is the point, of course, of the show’s recourse to folk. Loss in music: lost in music. The sound offers itself as a refuge when the usual words we exchange reach the limits of their usefulness. Hence their post-show gambit: a singaround in the Summerhall bar where we can propose, perform or just listen to songs that might rouse us back up into life again.

I’ve seen other comedy shows at this fringe address death: some good, some glib, but almost all two-dimensional next to Or What’s Left of Us. Today, at this unremarkable moment, you are in heaven, it tells us; a heaven to which one day you may long with all your heart to return. Not only does Or What’s Left of Us prove that Biscuit and Mothersole are still Sh!t Theatre, it proves that, like one of Louise’s beloved Japanese bowls, a broken Sh!t Theatre may just be more beautiful, more valuable, than ever.

• Sh!t Theatre: Or What’s Left of Us is at Summerhall, Edinburgh, until 25 August

• Brian Logan is the Guardian’s comedy critic and the artistic director of A Play, a Pie and a Pint