The Cosmonaut's Last Message, Donmar, London <br></br> Tristan & Yseult, NT Cottesloe, London <br></br> Hecuba, Albery, London <br></br> A Night At The Dogs, Soho, London

The telly is only emitting white noise in Vivienne and Keith's Edinburgh living-room. At work, Vivienne's speech therapy patients are groping for the right words. Then Keith himself doesn't even say goodbye, just leaving his clothes in a neat pile on the beach one night. In London, a Norwegian political negotiator, Eric, can't make his mobile work in the strip joint where, nonetheless, he swiftly picks up the Russian pole-dancer, Nastasja. Keith has previously crossed paths with her and become obsessed. Misinterpreting her husband's disappearance, Vivienne later travels to France and briefly hooks up with an ailing rocket scientist. But, up in orbit, Nastasja's despairing father and his fellow cosmonauts have lost all contact with the USSR and don't know it has expired.

Maybe the writer David Greig underlines once too often that failing communications constitute the key theme in these scenes from modern life (scripted in 1999). Some improbable plot developments arise as well. However, cavils aside and assuming you survive the title, The Cosmonaut's Last Message To The Woman He Once Loved In The Former Soviet Union is a beautifully written play - in fact, a minor classic. It is quietly probing while keeping the characters' motivations ultimately unknowable. Doubling further enriches the ambiguities as, for example, Michael Pennington plays both Keith and Bernard, a French UFO watcher. With alternating scenes, on earth and in space, Greig's narrative strands generate a sense both of isolation and of universal human experiences in love and loneliness. The dialogue can be startlingly comical as well, with veins of satire surfacing in exchanges that are also threatening or deeply pained.

Director Tim Supple's fine revival is haunting. The cosmonauts (in aerial harnesses) float above the stage, spinning against a black star-spangled sky (set design by Melly Still). Down below, Pennington is perhaps a tad self-conscious about his Scots accent, but he switches absorbingly from mild marital tetchiness to desperation and ardour. Tom Goodman-Hill's Eric has a disturbingly vicious streak. Brid Brennan struggles to be more than two-dimensional in her secondary role as Sylvia, Nastasja's possessive protector. However, she is excellent as Vivienne: a nervously polite wife with a resilient heart. Meanwhile Anna Madeley is superbly understated as Nastasja: mercurially innocent and craven. She is surely destined for major stardom, with the potential to be the next Julia Roberts.

Incidentally, Greig's new play, Pyrenees (currently at Southwark's Menier theatre), is an intriguing sequel to this, re-exploring what happened to Keith. As for the legend of Tristan & Yseult, the narrator in Kneehigh's adaptation turns out to be the romantic hero's sidelined wife. This physical troupe from Cornwall are always thrillingly imaginative and director Emma Rice sharply perceives this tale of extramarital ardour to be about the unloved as well. She even turns the spotlight on to the serving-girl, Brangian - who stands in for Queen Yseult in the bed trick played on King Mark - giving her a poignant soliloquy shot through with class anger and confused tenderness. It is also endearingly funny as Brangian is played by a galumphing cuddly bloke, Craig Johnson.

As for the passion of Eva Magyar's Yseult and Tristan Sturrock's Tristan, this is electrifyingly captured in a kind of acrobatic drunken ecstasy aboard ship. The set is like a wooden deck with a mast from which elastic ropes hang. Magyar and Sturrock, having knocked back the magic love potion like rounds of vodka, are hooked to these ropes like puppets and sort of dance - reeling and keeling - into each other's arms. It's a fantastic image of the irresistible pull of fate and sexual desire to which we also, willingly, abandon ourselves.

That said, the NT hasn't imported Kneehigh's most brilliant work here. Tristan & Yseult feels still like a work in progress, with Mike Shepherd's Mark ploughing through his rhyming couplets somewhat flatly. But the charting of damaged, dying and reviving relationships becomes increasingly searing, and Stu Barker's score and songs are an inspired fusion of folk and ethnic music, jazz and full symphonic surges. The near-operatic tragic ending is enormously brave.

If only the RSC had employed Barker to write the choric music for Hecuba. Alas, Euripides' formidable revenge tragedy, staged by Laurence Boswell and starring Vanessa Redgrave, only brings tears to the eyes because it is so gobsmackingly bad. Virtually everything has gone wrong here, and I'm not just talking about the dreadful events that Troy's former queen has to endure as a prisoner of war.

The modern reverberations are clear enough and Es Devlin's costumes suggest many a clan conflict, with Hecuba's chorus of women in headscarves and long ragged robes. But Darrell D'Silva is flailing as Odysseus, with a wobbly US accent, and to say Redgrave runs the gamut of emotions from A to B would, alas, be generous. It's as if she is stumbling around on the kind of pain-killers that are meant to stun a horse. Now that may, in fact, be the case as this acclaimed actress has, regrettably, been unwell. But the real tragedy is seeing her on such poor form and there's no excuse for others making Tony Harrison's forcefully alliterative translation sound like feeble doggerel. As for the composer Mick Sands, Greek tragedy is reduced to a dire West End musical with inauthentic ethnic chanting and much drumming thrown in - probably to drown out the sound of the audience's jaws hitting the floor in disbelief. Appalling.

Mercifully, A Night At The Dogs is far more enjoyable. This is darkening comedy about a bunch of clueless garage mechanics who've collectively bought a racing greyhound and are hoping make a mint. They've not reckoned on their violently psychotic boss, Paul, joining them. You've seen the basic ingredients before in other so-called lads' plays and mafia dramas. But this is an explosively funny first play by Matt Charman, who was working in a garage when he wrote it and has deservedly won this year's Verity Bargate Award. By the end, the conflict also packs a moral punch regarding bigotry, peer pressure and cowardice. The piece is, at points, too static and loquacious. Director Abigail Morris could still tweak some inert bits, but the swaggering wide boys and hopeless losers are splendidly fleshed out by Neil Stuke, Trevor Cooper, Mark Hadfield and co. Talent scouts from many a TV company will be tracking down Charman at high speed.

k.bassett@independent.co.uk

'The Cosmonaut's Last Message': Donmar, London WC2 (0870 060 6624), to 21 May; 'Tristan & Yseult': NT Cottesloe, London SE1 (020 7452 3000), to 7 June; 'Hecuba': Albery, London WC2 (020 7369 1730), to 7 May; 'A Night At The Dogs': Soho, London W1 (0870 429 6883), to 14 May