Brian Friel’s first big success, his evocative dream of leaving his native fictional town of Ballybeg in Donegal, was the prototype of the mid-century memory play, and it remains, like Tennessee Williams’ The Glass Menagerie, the early play with shadows and premonitions of the rest.

Not seen in London for 20 years, Lyndsey Turner’s pitch-perfect peach of a revival restores the poetic vibrancy of a play in which Friel’s Gar O’Donnell, on the night before he leaves for a job in a hotel in Philadelphia, revisits his own past in a divided identity.

Gar in Public is an accommodating, easy-going Paul Reid, easily led, shy of his own girlfriend, Kate Doogan (Laura Donnelly), and frozen in inexpressible love/hate for his non-communicative father, the crabby old store-keeper Screwballs (James Hayes).

Gar in Private, played with great verve, cutting edge and bubbling anger by Rory Keenan, in an identical V-neck maroon short-sleeve sweater and grey slacks with braces, is the inner voice, the voice of regret, goading and discovery. His face drops when he realises that the scruffy old teacher who wrote poems also wooed his mother – she died three days after his birth – and “might have been my father!”

Instead, old Screwballs pads miserly about the place, pre-programmed with a litany of banal phrases, mumbling the rosary and playing draughts with the equally mind-numbing local Canon (Benny Young). Their meals are served by Val Lilley’s lovely old housekeeper, Madge, whose circumscribed existence is blighted with its own disappointments.

It’s all so delicately, movingly done: Gar is the one boy of five Gallagher sisters, those five Glenties women Friel celebrated in one of his later great hits, Dancing at Lughnasa. He’s poised on the brink of escape, but he’ll never really leave. He recalls the vivid incursion of his aunt and uncle (Julia Swift in violent pink and Ruairi Conaghan in East Coast beige) who visit from Philadelphia and lay traps for him.

The emotional hinge of the play is the memory test of a fishing expedition in a blue boat, and the front door metaphorically slams shut when James Hayes delivers an unguarded, unprecedented emotional testimony not to Gar but to Madge. Anyone who felt he never got through to his (or her) father might be in pieces at this point.

There’s not a false note all evening, and the staging is impeccable on a wittily monumental design by Rob Howell that intersects the living area with the receding shelves of the store, packed with household knick-knacks and groceries, a museum-like display of boring essentials, bathed in Tim Lutkin’s lighting and the yearning strains of Mendelssohn’s Violin Concerto, the title song (ironically replacing California with Philadelphia) and Irish family favourites.