"I sometimes think my head may explode!" says Lyndsey Marshal about rehearsals for her new play, a West End revival of Three Days of Rain – and not without reason. Appearing alongside Hollywood star James McAvoy and EastEnders' Nigel Harman in Richard Greenberg's 1997 three-hander, the 30-year-old has found herself grappling with a dense, cross-generational script and two wildly contrasting roles – repressed New Yorker Nan and her mentally unstable, Southern-belle mother Lina. "Sometimes I think I know who Nan is, but not Lina. The next day, it's the other way round."
Then there's the hype to contend with: "I've never been in such a starry play. Whenever you see a poster on the Tube, you think they're spending so much money on it, you can't let them down."
Still, her anxiety belies her status as one of Britain's most dynamic young stage performers, as acclaimed for turns in Shakespeare, Molière and Miller as in bold new writing, such as last year's Royal Court success The Pride. On screen, meanwhile, she dazzled as a drugged-up Cleopatra in HBO's sex-and-sandals epic Rome, while last month BBC viewers saw her offer a more sobering turn in the docudrama A Short Stay in Switzerland, as the daughter of Dr Anne Turner, who committed assisted suicide in a Swiss clinic in 2006.
And next up? "I really don't know. I've got scripts but I can't bring myself to read them. I hate the connotations of being a resting actor, but you've got to go away and regroup sometimes, or you'll run out of anything to give."
'Three Days of Rain' is at the Apollo Theatre, London W1 (0844 412 4658 www.threedaysofrain.co.uk) to 9 May