AN Inspector Calls is one of those classic tales that everyone of a certain age knows. It has been adapted several times for the small screen – I recall sitting in front of the gas fire with my grandparents, watching a TV adaptation starring the inscrutable Bernard Hepton as the titular inspector; and is even a GCSE English literature set text, which might explain the number of young people in the Hall For Cornwall, Truro, audience.

And yet I’m ashamed to say I knew very little about the play’s history and its author, JB Priestley. The excellent programme notes filled in some gaps for me, explaining how Priestley was an ardent socialist and political activist, deeply disturbed by the social inequalities that were prevalent in Britain during his time, and which are brought to the fore in this, his most famous work.

Inspector Goole arrives at the home of the Birlings, a high-ranking family whose wealth has been built on industry. They are celebrating the engagement of their daughter to the son of a rival magnate.

The detective brings news of the grim suicide of an unfortunate young woman; one by one, each character is lured into admitting a connection with the victim, thereby revealing a viper’s nest of humanity’s worst attributes: spite, snobbery, jealousy, unaccountability.

This award-winning production, directed by Stephen Daldry (best known for films Billy Elliot and The Hours), is set during the war years. Sound has been used to great effect, most notably discordant music turned up to the max to suggest a threatening, overbearing presence.

The mood is sober, albeit lifted occasionally by Tim Treloar, whose inspector is commanding but often impudent. Welsh, angry and clearly of a lower class, he is relentlessly in the Birlings’ faces, seemingly above his station and yet always maintaining the upper hand over the puffed-up father, imperious mother, silly daughter and drunken son.

Mute extras represent the silent majority of the lower classes, gathering as the inspector delivers excoriating take-downs of the upper classes’ lack of responsibility or concern for those less fortunate.

The house itself is a masterpiece of set design: a tiny space symbolic of the cocoon the Birlings have built themselves from the outside world, only to be wrecked by revelations as destructive as the physical bombs of the time. It falls apart to dramatic pyrotechnic effect as the family is wracked by the ugly secrets now out in the open.

It’s quite a slow burner, a thought-piece rather than an action thriller, and it was occasionally hard to hear the all-important dialogue, especially when the characters were talking over one another (as angry people do).

I’m optimistic, nonetheless, that its messages will sink in over time and make a lasting impression. I’ve no doubt JB Priestley would be thrilled to see such a masterful performance of his words still captivating audiences 80 years on – although he might be saddened that we still need to be told.

An Inspector Calls continues until Saturday.