The Vertical Hour, Royal Court Downstairs, London <br /> The Sea, Haymarket Theatre Royal, London<br />Let There Be Love, Tricycle, London

David Hare's latest is thought-provoking but the plot rambles far and wide. All the same, it inspires some fine performances

It feels as if the cogs are slipping. We're surely juggling more than one jigsaw here. Certainly, on the subject of falling between four stools, wasn't he indicating left when he meant to turn right ...?

Like the above, The Vertical Hour keeps going awry. To sit through David Hare's latest work is like trying to follow a very long, very mixed metaphor. Granted, the play isn't totally incoherent and the fundamental scenario isn't very complex. Nadia (Indira Varma) is the beautiful and bright girlfriend of Philip Lucas (Tom Riley). He plans to marry her but has, unwisely, decided to introduce her to his father, Oliver (Anton Lesser). The young couple are staying at the isolated house (yes, that old chestnut) of Lucas père who is, we're told, a sneaky womaniser. Nadia is drawn to him, tiptoeing downstairs in the small hours when he stays up reading in the garden.

At the same time, this is a love-hate triangle with a political dimension. A major international conflict is, quite obviously, being played out in miniature. Though both of liberal stock, Oliver is British and Nadia is American. George Bush's invasion of Iraq happens to be his bugbear, and she is a war correspondent-turned-Yale politics professor who has backed the action to oust a murderous dictator. She is clinging to that argument, and it's known that she advised the President. So, in tandem with the sexual attractions, the ground is prepared for an ideological battle of words.

Oh, on top of that, did I mention that Nadia's bugbear is psychoanalysis, Oliver is a doctor, and Lucas fils is a physiotherapist moving into alternative treatments? Add Freudian theories and medical ethics to the catalogue of topics to be debated round the dining table.

Certainly, Hare throws up a clutch of thought-provoking points, while basically comparing personal and international relations, our private and our professional actions. Nonetheless, one can't help thinking that he isn't a natural dramatist. While on the one hand The Vertical Hour feels schematic – with its checklist of issues – on the other, the dialogue keeps skidding off whichever subject is fleetingly under discussion.

If we're going to have a play of ideas, could we please have a proper rigorous argument? Elisions can, of course, be dramatically intriguing but here they often feel like sloppy writing. Or if this play is meant to be a close study of the chatterati and the holes in their thinking – which are certainly worth looking into – could Hare not pen conversations that really ring true?

Actually, one or two of the longer speeches might have been lifted from background-research interviews but they, in turn, feel tacked on here. Consequently, the characters (as with the conversations) feel slightly like scrapbook composites or photofits. They never quite gel into the convincingly lifelike.

To be fair, Hare sets up some absorbingly contradictory traits in Oliver and Nadia. There is suspense – as well as humour – in the potential seduction. Lesser is slightly too desiccated, not sexily charismatic, but he does have chillingly edgy and ambiguous moments. You never quite know if he is a destructive patriarch or a dedicated medic.

Varma sends out subtly conflicting messages too: flirtatious and steely, almost spoiling for a fight. In fact this actress is superb and ought to be a major star. Director Jeremy Herrin has inspired sharp performances even if his setting – a mauve minimalist cube with a few silhouetted leaves – does nothing to combat the aridity of the play.

Vast surging waves are crashing over the stage of the Haymarket – projected on a giant scrim – in the opening storm scene of The Sea. One hopes this is a sign that Jonathan Kent's directorial residency at the Theatre Royal is gathering awesome momentum. Alas, I'm not convinced this is the case.

Edward Bond's period drama, written in 1973 but set in an Edwardian coastal town, is worth catching, though. It's disturbingly weird: a comedy of manners shot through with visceral menace and mournful despair. The seafront draper, Hatch (David Haig), is a closet loony, obsessed with the idea of an alien invasion. His xenophobia is twisted up with seething misogyny and class rage, so he goes completely insane – running around with shears – when a stranger arrives in town and his business is casually ruined by the haughty lady of the manor (Eileen Atkins).

The skeletally elegant Atkins is splendidly imperious. Marcia Warren is hilarious as her pea-brained sidekick when harmonising off-key during funeral hymns, and David Burke has profound serenity as the ramshackle old loner, Evens. But Ken Stott was a scarier Hatch in the NT production (with Judi Dench). Haig goes a bit Basil Fawlty.

The send-up of amateur dramatics is also a drag, not to say unwittingly ironic, given that Kent's own set and props were a liability on press night, from wobbling walls to a cudgel snapping in two and flying into the audience. Ah well, I guess Bond's reputation for shocking violence entered a whole new dimension.

Finally, the playwright Kwame Kwei-Armah specialises in portraying racism in all its rainbow hues. In his new self-directed chamber piece, Let There Be Love, he moves on from black-on-black tensions. Alfred (Joseph Marcell) is a testy old West Indian immigrant, long-settled in London, who gives his newly arrived Polish home-help, Lydia Leonard's Maria, a scornful hard time. But this is a tragicomedy, so they get to bond rather sweetly before the play tackles the issue of euthanasia.

Kwei-Armah's plot developments are creaky, but he does have a good ear and great affection for the quirky way people speak. This is a warm and moving play, mainly because Marcell's Alfred is mean but also lovable and Leonard is wonderfully natural, comically insensitive yet charmingly bubbly. Nice.

'The Vertical Hour' (020-7565 5000) to 1 March; 'The Sea' (0844- 844 2353) to 19 April; 'Let There Be Love' (020-7328 1000) to 16 February

Need to know

Sir David Hare, 60, is our best-known state-of-the-nation playwright. His NT trilogy – starting with 'Racing Demon' in 1990 – surveyed the Church, the judiciary and post-Thatcher politics. Later focusing on the Iraq war, he fell out with the National for not extending the run of his George Bush bio-drama, 'Stuff Happens'. So, 'The Vertical Hour' premiered on Broadway in 2006 ... but rifts heal. Hare directs 'The Year of Magical Thinking' at the NT this April.