Birdie is a hag, a harridan, a harpy – or that's what she's been told. Even glancing into the filthy windows of her stuffed-full house will suck out your soul. Just because she struggles to throw anything away, instead amassing it all in the teetering piles that fill every inch of her grimy home. It was those towers of tat that toppled to suffocate her aunt – or at least that's what the snooping authorities believe.

Just the presence of actor, comedian and, of course, national treasure Su Pollard as Harpy's solo performer inevitably makes her the focus of the show. And she delivers a fine, considered performance – sometimes a little deliberate – as a feisty elderly woman whose fragile grip on reality is fast becoming ever more flimsy.

But Philip Meeks's play is more than simply a vehicle for Pollard: it's a shifting, elusive piece, part thriller, part family tragedy, that asks pointed questions about our care for the elderly, and the ease with which we attribute blame to those we misunderstand or fear. Its gags – and yes, there's plenty of gentle humour – are occasionally rather obvious, and the ending feels a shade too heart warming for its earlier darkness. But Harpy is a likeable, deceptively provocative show all the same.

Underbelly Cowgate, until 26 Aug (not 13), 4pm, £12–£13 (£11-£12).