"Clamped together like limpets" they were, said campaigning journalist Marjorie Wallace, who told the story of "the silent twins", June and Jennifer Gibbons, diagnosed as "elective mutes", in a book and a television documentary.
It's an astounding story, and it makes for a riveting play in Linda Brogan's and director Polly Teale's adaptation, co-produced at the Traverse by Shared Experience and the itinerant Sherman Cymru.
The twins were sent to Broadmoor and burnt down their school. They felt stigmatised by their Caribbean origins, though their parents were well-adjusted Windrush immigrants: dad was in the RAF, mum loved the Queen.
Outwardly silent, inwardly creative, they played out royal scenarios in their bedroom, with their box of dolls. When Charles and Di got married, they went berserk: Mrs Gibbons (Anita Reynolds) coos at the royal couple in St Paul's while the girls embark on a drug-fuelled sex spree with a rich American kid.
Weird and disturbing though this is, we never lose sight of two severely disoriented teenagers who couldn't be coped with. They stay silent, then join a writing school and find their voices.
But the tragedy is not entered as special pleading: it's a story of stark and stunning oddness, played out against a backdrop of parental rows, baffled do-gooders and intuitive rage against the exploitation of women; and if that sounds too "right on" for comfort, I suggest submitting yourself to this brilliant, bleak, but redemptive production.
To 29 Aug (www.traverse.co.uk)