The Trial of Ubu, Hampstead, LondonThe Madness of George III, Apollo, Shaftesbury, LondonShallow Slumber, Soho Upstairs, London

A century on, an aburdist tyrant is put on trial at last; George, meanwhile, struggles to get the measure of Alan

King Ubu is a glove puppet going psycho. In the prologue to Simon Stephens's new play The Trial of Ubu, as staged by Katie Mitchell, this miniature scabrous clown, resembling Mr Punch, zips around in a sharp-edged square of light.

Spouting obscenities, he's like a brat with coprolalia, or Freud's id personified on a wildly amoral spree. He's also a despot in the making.

The prologue is, in fact, a condensed version of Alfred Jarry's proto-Absurdist shocker, Ubu Roi, from 1896. So we see Ubu bump off King Wenceslas, seize the crown, then blithely oversee the disappearance of the realm's judges and top-hatted bankers, plus any plebs resisting his taxes. Everyone is tossed over his shoulder, into oblivion.

Suddenly the puppet-play portal snaps shut, and a larger, life-size window slides open in Lizzie Clachan's superb set – a towering wall fronting the stage. In a bold shift, it's now the 21st century and the actresses Kate Duchêne and Nikki Amuka-Bird are sitting in a hushed translation booth with headsets and microphones. They are interpreters, perched above an international tribunal at The Hague where, we gather, Ubu stands accused of crimes against humanity.

Mitchell makes this very low key, with a nod to the Tricycle's tribunal plays but, to boot, putting the proceedings at one further remove by having Duchêne and Amuka-Bird relay everything the judge, lawyers and witnesses say. What's enthralling is how the women's tone of voice – quiet and cool – is belied by physical intimations of tension. Amuka-Bird moistening her mouth with a spray. Duchêne seems steadier. However, as graphic descriptions of mass graves leak into the arid legalese, she halts, as if unable to suppress sobs. Or is she, unnervingly, laughing? It's a brilliant stroke of ambiguity when Duchêne's character develops a heavy cold: merely a medical irritation, yet one that makes her sound tearful.

To what extent are these interpreters detached? Are they twitchy just because it's a high-profile case? Alternatively, are they humane and thus finding the evidence harrowing? Or might they each be harbouring undeclared biases? The Trial of Ubu raises questions about disinterest, including the border line between the judiciously neutral and the damnably callous. Both actresses are terrific, also creating time-lapse scenes where they mouth silently at surreal speed, while their bodies jump and jerk.

Nonetheless, Mitchell's hints of enigmatic menace can end up looking like obscure loose ends. There are comparatively lame scenes on the sidelines too: a jailer effing at a frail Ubu (Paul McCleary); off-duty lawyers in a wooden altercation. Oh, and did I mention the puppet play's dark farce falls flat (its direction delegated to cast members)?

In Alan Bennett's much-loved history play The Madness of George III, David Haig's George is a jolly decent fellow, loyal husband and responsible ruler. That's until he goes insane, aged 50, suffering from what would, today, probably be diagnosed as porphyria. His body is wracked by burning pains and incontinence, while his behaviour degenerates into infantile rages, Ubuish splurges of rude words, and much shameless lusting after his wife's Lady of the Bedchamber. While casting off all self-restraint, Haig's George has also been fretting about the control he's lost over the American colonies, and the Prince of Wales, who's a power-hungry, heartless fop.

This is an intriguing royal portrait: comical, tragical, political, somatic and psychological. A gaggle of grandiose quacks exacerbate his torments with purging and blistering. Finally, a provincial ur-psychotherapist (a bespectacled Clive Francis, with a touch of Bennett) forces the unruly monarch to obey his strictures, and thereby George learns to govern himself again.

Christopher Luscombe's production is handsomely staged in period costume, but with much milking of Bennett's quips and echoes of King Lear when a lighter touch would better serve. Some of the supporting cast also waggle around on the apron stage peculiarly like marionettes, unable to determine if they should address each other or the audience.

In Soho Theatre's studio space, a dangerous blast from the past has turned up on Moira's doorstep. Amy Cudden's gamine Dawn is just out of prison and wants her ex-social worker to let her in; Alexandra Gilbreath's Moira isn't keen. They stand locked in a battle of wills in Shallow Slumber, a two-hander by rising playwright Chris Lee, played out on a narrow, shadowy strip of stage in Mary Nighy's claustrophobic production.

Once over the threshold, Cudden sits hugging her knees, beaming with relief, but perhaps with a glimmer of threatening triumphalism. Unkempt in her dressing gown, Gilbreath glares balefully, though prone to be a soft touch. Lee's play (drawing on his own career in social work) moves backwards through time, exposing both women's scars. The script could do with some stern paring, but Nighy and Cudden are names to watch, and Gilbreath is searingly good.

'The Trial of Ubu' (020-7722 9301) to 18 Feb; 'The Madness of George III' (0844 412 4658) to 31 Mar; 'Shallow Slumber' (020-7478 0100) to 18 Feb

Next Week:

Kate Bassett will be in attendance at She Stoops to Conquer at the NT

Theatre Choice

Rafe Spall and Sally Hawkins are droll and heartbreaking in Constellations, Nick Payne's looping portrait of a love affair replayed in parallel universes, at London's Royal Court Upstairs (to 11 Feb).

The new nanny is a sinister spanner in the works in Our New Girl by Nancy Harris, at London's Bush Theatre (to 11 Feb).