Insignificance is famously the play in which Marilyn Monroe gets to explain the Special Theory of Relativity to Albert Einstein. Shortly after, the great scientist imitates the screen goddess by showing his legs - why, he's even wearing suspenders. Terry Johnson's 1982 Royal Court success -- which also has roles for Senator Joe McCarthy and Monroe's baseball star husband Joe Dimaggio - was one of the first plays to feature well-known figures in odd conjunctions. The same playwright's Hysteria (Freud/Dali) and various works by Caryl Churchill, Michael Frayn and Tom Stoppard belong loosely in the genre too. Frayn and Stoppard, like Durrenmatt before them, also present scientific debate of the sort tackled in Insignificance.

The intellectual content of the play invites those watching it to consider themselves intellectual. Two people behind me in the stalls at the Royal on Tuesday night chose to advertise their brilliance - their recognition that this was a play for first-class brains only - by laughing like hyenas at lines that deserved only a thin smile. Their vulgar intrusions must have spoiled things for many members of the audience.

Free of such distraction, Rupert Goold's production is one of considerable power that thoroughly confirms his belief, spelled out in a lucid programme note, in the staying power of the piece. As he says, though the Cold War is over, there is still an 'us and them' paranoia in US foreign policy and more interest in the nature of celebrity - which is the play's main theme - than ever before.

The setting is a hotel room in New York (fine stars and stripes design from Ruari Murchison) where we find Paul McCleary's wild-haired 'Einstein' (none of the characters is identified by name, incidentally) preparing for an appearance at a peace conference. His pottering among his papers is interrupted by the arrival of the thuggish McCarthy (Alan Perrin), who is demanding his appearance at his House Un-American Activities Committee. Scarcely has he left, than MM (Gina Bellman) arrives, escaping pursuing fans, with aggressive husband Joe (Steven Hartley) not far behind, and more than a mite curious about what his wife is doing in another man's bedroom at 3am.

Reality and fantasy are judiciously combined in what follows in this enjoyable and generally well-acted production. Ms Bellman is particularly good as Monroe, though a curious Eastern European twinge to her accent marred early scenes on Tuesday.

The play continues until May 15 (box office tel: 01604 624811).