Just reading through my review notes on this show makes me feel quite exhausted. "Keynesian economics", "trade deficit", "IRA hunger strikes": you see, the "little madam" in question is a certain Margaret Roberts.

Anyone who knows anything about this particular life knows Britain's first woman Prime Minister packed a lot in and therefore that any dramatist, no matter how talented, in is danger of drowning in detail.

Much like Thatcher's reign itself, James Graham's play goes on far too long. It's an alarming moment when, at 10.15pm, we realise we're still in 1983. Thanks to Graham's nifty structure, though, we're also still in 1937, with the 12-year-old Margaret banished for insubordination to her bedroom above her father's grocery store in Grantham. A stash of anthropomorphic toys, the only companions for this stern, frowning child, are passing the night providing snapshot glimpses of a startling, intransigent future.

Just as in life, Maggie's opponents here - Bobby Sands, the Archbishop of Canterbury, a miner - aren't any match for her, which sees Graham, and therefore director Kate Wasserberg, struggle to sustain interest as she steamrollers ever onwards through increasingly schematic scenes. Apart from a spot of eyelash batting at Cecil Parkinson and his rakish selection of ties, it's privatisation as usual.

Nonetheless, Catherine Skinner gives a magnificent central performance that ranges from occasional girlish giddiness to unturnable lady of iron. It's a shame that work as good as this will get overlooked in the forthcoming awards flurry.

As for Graham, at only 25 his potential is undisputed. Let's just hope his toys advise him to be more concise next time.

• Until 27 October. Information: 0870 4000 838, www.finboroughtheatre.co.uk.