Two of Ireland's finest actors, Anita Reeves and Stephen Brennan, play two elderly inmates of a nursing home in this tender and acutely observed 70-minute two-hander by Deirde Kinahan.
In American theatre terms, this is On Golden Pond or Driving Miss Daisy territory, but the give and take between Reeves' retired primary school-teacher, Patricia, and Brennan's quavery old actor, Sean, is steeped in their Irish locality and peculiar reticence.
Patricia has cirrhosis of the liver - not from drinking, she emphatically points out - while Sean is trembling with Parkinson's disease; she is a spinster who lives with her sister, he a discreet homosexual lately deserted by his partner but floating on good memories and Shakespearean quotations. Both are from farming families in the Republic.
What could have been an over-schematic coming-together in David Horan's production, especially when the two of them become mobile and teary-eyed to the accompaniment of Patricia's classic film score tapes, is in fact a very touching development of friendship between two needy people.
And there's a harsh injection of reality when a mis-timed lunge at closer physical contact leads to a frank assessment of Patricia's situation at home and a decision - an unexpectedly drastic one - taken on how best to deal with her rapidly declining health.
Reeves, with her large and watery eyes, plays her loneliness directly and piercingly through every line, while Brennan reveals himself more gradually, neither succumbing to mawkishness; it's a master class from the two of them in subtle, inflected emotionalism, a sad and deeply affecting duet in the twilight zone.
These Halcyon Days continues at Assembly Hall until 25 August (not 7, 12, 18)