"I am what I am, a 42-year-old pock-marked Jew fairy," declares Mark Gatiss's Harold, the birthday boy guest of honour at a New York party in 1968.

This was a time when gay life could only be lived openly indoors, a year or so before the Stonewall riots, which told the world that America's civil rights movement had a gay wing.

So every expression of gayness in Mart Crowley's groundbreaking play - before which gay men were generally depicted as loners tormented by an unspeakable affliction - has to be seen in that context, even when it leans a tad too heavily on the tropes and conventions we sometimes call stereotype.

With that reservation, Adam Penford's terrifically acted, rare revival is a lot of fun. Populated by seven gay men who arrive at Michael's (Ian Hallard) New York pad to celebrate the birthday of the razor-witted Harold, the play's tension is derived from the unexpected arrival of Michael's former (straight) college room-mate Alan, an educated alpha male who personifies the increasingly liberal but still intolerant society of the time.

Should Michael and his guests suppress their sexuality in an attempt to save themselves from Alan's judgment? Emory (James Holmes) part doting mother and part waspish aunt, couldn't do that if he tried - which he doesn't.

Driven by Michael's alcohol-fuelled mean-mindedness, the evening unravels when the host imposes a game of truth-telling on his guests, even on the unwanted Alan (John Hopkins) who, in Crowley's clever, table-turning conceit is the only straight man in the village.

Nearly half-a-century after its premiere, the plot twists are all easily anticipated. Yet Penford's production crucially captures the mood of the time and the sense of a sensibility and culture being unleashed.

It also serves as reminder of not only how far society has come, but how far we still have to go.