I’m still not sure what to make of The Dazzle – in the least comfortable fringe theatre newly created in the West End, up 76 steps and with a padlocked lift the first mystery is how Westminster Council licensed it. It starts out as quite a tender portrait of a brother caring for his spectrally introverted concert pianist twin but in Act 2 turns in to Grey Gardens without the jokes, the music or the outré ways to wear a cardigan.

It could have influences of Booth Tarkington and Henry James, or, given the audience’s urgent willingness to laugh at every line in the first ten minutes, it could be the biggest pile of pretentious crap which if you paid thirty-five quid to sit on a junk shop chair in an unheated attic you’re not readily going to admit. But I loved author Richard Greenberg’s The American Plan when I saw it at the St James’s so I’m giving him the benefit of the doubt.

It’s a masterclass in ‘real acting’. It may be Andrew Scott’s ‘Moriarty in Sherlockcredentials that have pulled this crowd and for sure he gives good psychotic, with entrancing finesse in his petulance and incipient danger in his affection – but for his nervy narrative and perfectly rationed transition from whimsical sardonic to blind tearfulness it’s David Dawson who claims your equal attention, and for whose character you eventually weep.

The actors’ similarity and parity of skill makes fraternity completely credible: Langley and Homer Collyer were wealthy-born eccentrics who holed up in a brownstone house in Harlem at the once-smart corner of 5th Avenue and 128th street. As their distaste for the changing demographic of the neighbourhood increased, they barricaded themselves in with 140 tons of assorted bric-a-brac, booby trapped the entrances and were eventually found dead, decomposing corpses crushed by the debris.

Their transition from privileged patricians to slatternly hoarders in a danse macabre precisely presages that of Edith and Edie Bouvier Beale. Greenberg‘s script neatly charts the changes in the brothers’ situation and relationship, specially fine in its handling of Homer’s failing sight and Lang’s autistic relationship with the opposite sex in the splendid form of Joanna Vanderham as a society heiress, although having her also mutate into a vagrant is less convincing.

But, just like Grey Gardens, it fails to explain WHY the characters found it impossible to do a stroke of housework for forty years.