Richard Nelson has stolen his title for his elusive new play about Harley Granville Barker in America from the short play Granville Barker wrote in 1916 before going into the army; he’d already served with the Red Cross in France and made his reputation as the outstanding actor, director and playwright (second only to his great friend and colleague, Bernard Shaw) of his day.

Granville Barker’s two-hander shows an actress on the brink of discovering that theatre must change and that “truth lives where only other people are.” Nelson gives us a portrait of Granville Barker (Ben Chaplin) at a similar crossroads in a boarding house in Williamstown, Massachusetts, where he is renewing his faith in theatre.

But his life is complicated by his separation from the actress Lillah McCarthy and his new attachment to Helen Huntington, neither of whom appear in the play, alas. He is being sounded out for a job in the university, and he’s on a lecture circuit with a Dickens specialist, Frank Spraight (Jason Watkins, suitably Dickensian).

He becomes embroiled in university politics and a conflict between amateur and professional theatre represented by the sad ambitions of a thwarted professor, Henry Smith (Louis Hilyer), and a bumptious star turn in the college Cap and Bells society, Charles Massinger (William French).

What is in effect a sober conversation piece with insider historical information is presented with stark clarity in Roger Michell’s admirably cast production, on a bare boarded set (by Hildegard Bechtler) that obliterates the division between stage and audience, much as Granville Barker did away with the footlights in his day.

But the flame of the play, and of Ben Chaplin’s performance, burns quite low, ending in an almost embarrassingly unremarkable Mummers Play in the garden, suddenly lit in full sunshine (by Rick Fisher) with a glimpse of summer trees beyond. Granville Barker has rediscovered that theatre matters, but this is all talk, not show, and it’s a struggle to remain interested for the uninterrupted 105 minutes’ playing time.

Still, it’s very good to see Chaplin on the stage again. Jemma Redgrave as the widow manageress, Henry’s sister, emotes quietly in the background and Tara Fitzgerald as a flighty lecturer impresses once again with her ability to inhabit any period or indeed costume without seeming false or unnatural.

As a testament to Granville Barker, the play is obviously positive but also too knowing for an audience unaware of his then radical, now taken-for-granted, approach to Shakespeare. And as a study of English people dislocated from their home culture “on the edge of the earth,” as Frank puts it, well, we have to take their word for it.