Physicist Werner Heisenberg’s eponymous principle states that the more precisely we measure a particle’s position, the less precisely we can measure its momentum, and vice versa. Giving your play a title like that is an immense hostage to fortune; Simon Stephens must have steeled himself for a lot of glib comments about where his play and characters are going and so forth.

The 85-minute piece begins in medias res. Alex, a 75-year-old butcher sitting meditatively in St Pancras station, has just been kissed on the neck by American-born Georgie, 42, who has mistaken him for someone she once knew, now deceased. That last detail is typical of Georgie’s mind: she seems not so much to have trains of thought as trampoline routines. She dominates the conversation almost entirely at the beginning, but over days and weeks the two grow closer both emotionally and in terms of word count. Staid Alex, seemingly settled into the autumn of his life, knows where is he is but Georgie’s arrival takes him by surprise as regards where he’s going; she, on the other hand, always knows she is somehow or other going to New Jersey to try to track down her estranged teenage son, but the moment-to-moment aspect of her relationship with Alex is likewise unexpected for her. They are, if you like, negotiating a mutual arrangement whereby each factor is tolerably well known to both, as a kind of working basis.

The production is billed as a reunion of the team behind the successful The Curious Incident Of The Dog In The Night-Time: Stephens (who adapted Mark Haddon’s novel), director Marianne Elliott and designer Bunny Christie. This is a prime pedigree, and is only enhanced by the presence of those twin masters Kenneth Cranham and Anne-Marie Duff as Alex and Georgie. The only odd touch is in scene transitions, as walls and lighting of Christie’s spare set move around to reconfigure the imagined space: in these brief sequences, Cranham’s movements seem a little self-conscious, as if he were not at home in an abstract environment. The piece overall, too, feels moderately wacky by West End standards but restrained on Stephens’ terms, as if he were either testing how far he can take a mainstream enterprise or simply dealing discretely with two different constituencies, here and in his more characteristic work. Perhaps the play itself is conducting the same kind of negotiation as Georgie and Alex.

Written for the Financial Times.