Guess who hasn't come for dinner

The Guests/ Goodbye Kiss | Orange Tree, Richmond Tae | Union Chapel, London

There's nothing like having Harold Pinter in the audience to give your first night that extra something. At the Orange Tree on Tuesday, the great man's slightly glowering presence briefly made the end of the District Line seem like the centre of the theatrical universe.

The UK stage premiÿre of two one-act plays by Ronald Harwood might be said to constitute a major event in its own right. The South African-born playwright's ability to fashion sturdy, commercially viable dramas has become pronounced of late (two West End runs, Taking Sides and Quartet, in the last five years) and is all the more impressive for his having reached retirement age. If anything, though, Pinter's attendance inadvertently pointed up how mild Harwood's work can sometimes be.

The act of pairing The Guests - a 1972 TV monodrama - with a 1997 radio play, Goodbye Kiss, invites comparison with the recent bundling of Pinter's first and latest numbers (The Room/ Celebration) at the Almeida. That juxtaposition was generally judged fruitful - an opportunity to look at thematic continuity and career trajectory. In Harwood's case, however, you're left to marvel that 25 years' experience doesn't improve the odds against having an off-day.

The Guests centres on an unnamed woman who hosts a dinner party attended by imagined interlocutors. What starts out as nattily one-sided takes a turn for the transparently deranged. The woman is on edge, suspicious of her own family - her sister-in-law and sister and their husbands - for fear of being sectioned. With the arrival of an unexpected guest, an "electrician", the talk alights on the "sparks" treatment that has jumbled her mind.

Janine Ulfane brings considerable energy to the part, nicely capturing the woman's nervy disorganisation - her feet performing a shy, restless shuffle. But she doesn't have the power to bring the character alive, partly because she never makes you see the guests; she doesn't seem seized by their reality. The visitors are convenient prompts, permitting hasty expressions of a mental collapse that is never satisfactorily explained. The piece might have fared better had director Joe Harmston done a Pinter and slowed things down a little.

Goodbye Kiss is brief to the point of underdevelopment. This autobiographical two-hander recalls Master Harold and the Boys, in which Athol Fugard dwelt on the shaming childhood moment when he spat in the face of a black servant. The bitter memory in this case concerns the central character's failure to kiss his nanny in public upon embarking for England.

Returning to Cape Town 30 years on, Donny finds racial hurt lurking beneath the pleasantries of his reunion with Annie (a richly conflicted performance from Denise Newman). She is unimpressed by his émigré anti-apartheid demos, and refuses the chance to kiss and make up. It's a simple enough insight into the way griefs nursed over a lifetime can't be reconciled at the drop of a hat - but none the less powerful for that. Yet I wish that Harwood had drawn the 20-minute scene out; so much more could be said.

A greater ability to spin a show from the slenderest story is to be found at the gloomy Union Chapel in Islington, where London is getting a rare taste of contemporary Korean theatre. Written in 1974 by T'ae-sok Oh, one of the country's foremost playwrights, Tae relays a brutal episode from Korean history. In 1456, Se-jo, the uncle of Danjong, the 15-year-old king, usurped the throne and proceeded to deal with the subsequent rebellion of the kingdom's scholars by executing them and their extended families. As you do. The play charts the birth of a qualified kind of hope: one of the scholars' wives, Lady Park (Junghwa Lee), saves her newborn son by swapping him with a servant's son.

Director Gina Lee and choreographer Aesoon Ahn flatter an unenlightening combination of Korean and English texts with a visually striking, if sometimes unsteady, mix of synchronised movement, dance and martial arts. The weirdest and wildest moment is when Lady Park and her servant are lain foot to foot in a prolonged bout of thrashing labour to an ear-busting din of ravey oriental percussion and cymbals. An aura of cruelty and beauty surrounds the androgynous figure of Wai Kit Tang's Se-jo, who is almost out-pouted by the stern multi-racial supporting cast.

'The Guests'/'Goodbye Kiss': Orange Tree, TW9 (020 8940 3633) to 3 June; 'Tae': Union Chapel (020 7226 1686)to 14 May