The Glass Cage, Royal & Derngate Theatre, Northampton

A taut drama of family fortunes

Not all theatrical rarities are worth unearthing. This one resoundingly is. The Glass Cage is a play by JB Priestley that has not been performed since its one and only London run in a production that hailed from Toronto 50 years ago.

Following the kind of slump that hits artists in the immediate aftermath of their death, the Bradford-born sage's stock took a sharp upward turn with Stephen Daldry's expressionist and emphatically socialist take on An Inspector Calls, which was an international hit in the 1990s.

The notion of Priestley as a much more various and experimental writer than is generally acknowledged was consolidated by the major retrospective masterminded by Jude Kelly at the West Yorkshire Playhouse in 2001.

One of the big successes of that season was a sleek, biting, contemporary slant on Dangerous Corner by Laurie Sansom. As artistic director of the beautiful Royal & Derngate Theatre in Northampton, he now makes a splendid job of breathing highly imaginative life into The Glass Cage, a piece that was given a tantalising rehearsed reading in Leeds.

It here receives a full staging that is scrupulously in-period and alert to social nuance (the Canadian accents are all spot-on), and yet, with its open-to-the-elements set, also keenly alive to the unsettling eeriness of the forces that blast apart the claustrophobic surface respectability of this upper-bourgeois Canadian home in 1906.

You don't expect to find a Priestley play located in Toronto, but while it may be a far cry from England geographically, in terms of theme The Glass Cage has certain strong affinities with An Inspector Calls. But instead of a police inspector who is genetically morally independent of the investigation that springs family skeletons from cupboards, the catalytic characters are connected by more than ties of blood to the well-heeled Edwardian hypocrites they are determined to rumble.

They are the three estranged young adults (two nephews and a niece), who are the fruit of their father's long relationship with a Native-Canadian woman. To the sounds of a ghostly wind, the trio parade like enigmatic conspirators into the upholstered household with its uptight piety, and its prayer-meetings, and its clan that consists of an aunt (Janice McKenzie) whose guilt has turned to on-edge hostility, her whimsically venal and vindictive brother (Robert Demeger), who ruined a man to gain a mistress, and the head of the household (John Arthur), a pious martinet whose genuine Christian instincts are warped by the duty of hushing up the sins of his siblings.

The family wants these mixed-race visitors to sign a deed of transfer, just as, years before, their father had been prevailed on (in dubious circumstances) to make a disadvantageous deal. The newcomers have had chequered, humanisingly hand-to-mouth careers and are soon turning the drawing room into a raucous saloon. The scene in which they seductively embroil their two upright cousins in a wild, drunken romp is played as a stamping danse macabre. That is in keeping with the increasingly double-edged nature of the drama.

The performances are wonderfully well-judged. A star-in-the-making, James Floyd brings a serrated edge of mocking, cockily comic challenge to the bibulous, impulsive younger nephew, while Dar Dash expertly radiates the strained containment of his older brother. As their sister whose jobs have included dodgy, customer-oriented theatricals, Rebecca Grant luminously communicates the drop-dead wit of this precocious young woman and registers the acumen that allows her to see that the deepest injury that the family has done them is not financial, but the instilling of a habit of hatred. That is the glass cage of the title and it's a prison from which self-transcendence is the only means of liberation.

Priestley's play hit the theatre at the time of the Angry Young Man explosion. Helped by a revival of this calibre, you can see how it yields to none of the works of the period in its trenchant subversiveness.

To 17 November (01604 624811)