The Curious Incident of the Dog in the Night-time, Cottesloe NT, London Philadelphia, Here I Come! Donmar Warehouse, London Much Ado About Nothing, Courtyard, Stratford-Upon-Avon

The best-selling novel about a sleuthing boy with Asperger's syndrome loses something in adaptation, yet still moves

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Habitually twisting the drawstring of his hoodie, Luke Treadaway's pale, skinny Christopher has Asperger's syndrome. The troubled teen hero of The Curious Incident of the Dog in the Night-time – Mark Haddon's hit novel, newly dramatised – screams if anyone touches him, and he can't understand others' emotions. Yet he likes hard maths questions, survives domestic traumas and solves a murder-mystery.

Staged by Marianne Elliott on a giant, star-spangled blackboard, with mimed and danced episodes (choreographed by Frantic Assembly), The Curious Incident can feel like cloying kidult edutainment, sentimentalising Christopher's obsessive interest in science. Though Simon Stephens's adaptation takes few liberties, the all-important tonelessness of the novel's first-person narration is lost, Christopher's notebook being read out by his caring teacher (Niamh Cusack).

Nonetheless, Treadaway – intensely insular, yet touching and funny – is superb, and so are Paul Ritter and Nicola Walker as his fraught parents.

In Philadelphia, Here I Come! – Brian Friel's early play, from 1964 – Gar O'Donnell's father has emotionally atrophied. He is dead behind the eyes, or so his son believes. The 25-year-old is sick of small-town Ireland where he toils in his widowed da's dry-goods store. He's flying to America tomorrow. If he stays, housekeeper Madge, reckons, he'll end up as desiccated as his old man.

Gar has such a full inner life right now that there are, in fact, two of him on stage. Rather than soliloquising, Friel's pent-up protagonist has a double who constantly voices his unspoken thoughts. In director Lyndsey Turner's revival, Paul Reid plays the "public" Gar while Rory Keenan's "private" Gar hovers nearby, chatting away, in identical tank top and grey flannels – sometimes perching on the shop shelves which stretch on and on up the back wall, above Gar's sliver of a bedroom (design by Rob Howell).

When Reid is downstage, in the spartan dining room, enduring supper with his dour, taciturn father (James Hayes), Keenan bobs at Reid's shoulder supplying a satirical running commentary. He is the vital impish spirit, invisible to others, who prevents Reid – and, of course, the audience – from being bored rigid. Keenan's private Gar can also be seriously pained, expressing desperate yearnings for parental affection.

This play made Friel's name internationally, and his doppelgänger set-up surely influenced Peter Nichols' Passion Play and Alan Bennett's The Lady in the Van (with two Alans on stage). The Gars are complex, and the piece is multilayered, moving between present reality, daydreams about the future, and regretful flashbacks.

Philadelphia, Here I Come! can, for all that, occasionally seem schematic and underdeveloped. Turner's production also needs more varied tempi. The intention is presumably to be instantly engaging, but th ere is an excess of motor-mouthed perkiness and insufficient bleak silence.

The ensemble is commendable, nevertheless. Keenan is assured, increasingly winning, and has one memorable, poignantly still moment – singing a melancholic Irish ballad. Valerie Lilley's aged Madge is absolutely wonderful as well, spindly and shuffling, yet with a lively wit and deep-seated tenderness.

The RSC's new Much Ado About Nothing, translated to modern-day India, hasn't been properly paced by director Iqbal Khan. On top of that, his cast's acting is disappointingly patchy. Paul Bhattacharjee's gangly, greying Benedick seems nice enough, gaining dignity when this comic romance darkens. His old flame, Meera Syal's Beatrice, begins charmlessly, more sour than funny, although maybe that's a brave choice, and it is backed up by textual references to her shrewishnesss. The trouble is, once these two succumb to falling in love again, they only sporadically convey any chemistry.

You know something has gone very awry when the show is stolen by an expanded bit part: Anjana Vasan playing a sweetly naïve maidservant who veers between wildly liberated dancing and cowed meekness.

The Indian setting could be a strikingly snug fit, as well as being gorgeous to behold with embroidered silk turbans and spangled saris. The uncertain limits of women's liberties in Leonato's household are highlighted: especially so when this patriarch, too readily believing his daughter Hero is unchaste, virtually wishes an honour killing on her. ("Death is the fairest cover for her shame.") The programme notes also underline how her betrothed is a soldier struggling to adjust to civilian life, but as played by Sagar Arya (in a blue UN beret), Claudio's outbursts of violence look like schoolboy scuffles. More training needed.

'The Curious Incident of the Dog in the Night-time' (020-7452 3000) to 27 Oct; 'Philadelphia, Here I Come!' (0844 871 7624) to 22 Sep; 'Much Ado About Nothing' (0844 800 1110) to 15 Sep, then Noel Coward, London, 22 Sep to 27 Oct

Critic's Choice

Alecky Blythe’s bravely experimental, outstanding documusical London Road, recording local residents’ reactions to the 2006 serial killing of women in Ipswich, returns to the National Theatre in London, where it started in the Cottesloe, and transfers to the larger Olivier stage (to 6 Sep). Gregory Doran’s not-to-be-missed RSC Julius Caesar, set in modern-day Africa and with a superb ensemble, is now in the West End at the Noel Coward (to 15 Sep).