Merlin (Nuffield, Southampton)

"Read. Always read." Writers Ollie Birch and Ella Hickson reset Arthurian legend in a vast library, making a hero of its bookish boy-wizard in the process. Framed as an amateur production by a stack of librarians, all top to tail in tweeds and tartans, taking tea breaks at every turn (oh England, my England), their Merlin tries to stress the magic of the written word – not just that stories can make whole worlds materialise, but that they can change the one we're in for real.

It's a subtle piece of literary criticism – probably too subtle for an audience of over-fives. Birch and Hickson tweak the tale so that Lady Guinevere, or Gwen (a hearty Kayla Meikle), does more saving than being saved. She's not tied to the stake but charging down the dragon herself. Meanwhile, Adam Welsh's clumsy, clownish Merlin discovers a courage of his own, as his spells prove more effective than others' swords.

As a result, Fred Lancaster's Boy's Own Arthur, his chest puffed to bursting, finds his presumptions overturned, but without emphasising the rewrite, there's a chance that children might miss the point: that the way girls and geeks are portrayed on the page affects the way they're perceived in the world.

That only really registers in the subplot, as Arthur's promised princess (Aryana Ramkhalawon) realises life doesn't play out as prose would suggest. Her dream wedding, documented in a scrapbook heaving with handsome princes, OTT dresses and piglet pageboys, falls apart.

Will the kids miss the gender politics? Not likely. Liam Steel's production has too much to offer: plenty of tricks to amaze young eyes, some gorgeous puppetry and a host of characterful performances. Welsh's Merlin, in his knitted tank-top and red bellbottoms, is superb: unworldly in every way, as he bumps into bookshelves. He comes of age with real control. You hardly notice him growing up until he's standing tall at the end. Joshua Manning is more than och-aye as a Scottish king, while Rob Castell instils a real comic kick as a pompous French suitor who rocks up in a thigh-high kilt, then a chainmail onesie. His songs, though occasionally overly wholesome, add bounce and verve.

Admittedly Steel and his designer Yannis Thavoris might have committed more fully to the library setting, using books and reading lamps to set the scene. As it is, their company of librarians seem to have the budget and stagecraft of a decent regional rep – despite the setting's emphasis on imagination. Even if it owes more to money than to magic, Thavoris's stage is enchanting nonetheless: sky-high shelves and towering ladders with gorgeous costumes all round. Likeable, not legendary.

Merlin runs at the Nuffield Theatre until 3 January.