The obsessive narrator at the centre of Blinded by the Sun, Stephen Poliakoff's second play this year, has a beard, low-slung trousers and a pen sticking out of the front pocket of his corduroy jacket. He is - no, don't say obviously - administrator of the chemistry department at a Northern university. All this is quite normal: what isn't is the way he hangs on to his past.

We know Poliakoff likes obsessives. His last play, Sweet Panic, which premiered at Hampstead seven months ago, has a mother stalking her child's therapist with a file of newspaper clippings. In Blinded by the Sun, the narrator, Al, introduces scenes by pulling transparent bags out of wooden lockers and taking out what he has saved for posterity - ginger biscuits, barley sugars, ear-plugs, baking powder or a fork stolen from the Garrick Club. There are hundreds of bags inside these lockers, strung together in chronological order. He has even colour-coded them. He should be stalking the therapist in Sweet Panic. He needs help.

Poliakoff's witty and stimulating play addresses the way success distorts scientific inquiry. As a form of inquiry itself, Blinded by the Sun is less than scientific: it resembles a highbrow discussion programme - intelligent, informed, concerned, but unfocused. In a play where evidence is crucial, it suffers from its own implausibilities.

As played superbly by Douglas Hodge, Al has a snuffling, cheeky nerdishness that turns into a monstrous callousness. He wants to change the department's name to "Energy Studies". He publishes anti-science bestsellers (titles include Beware of the Experts). Eventually he closes down the department. This means ending a lifetime's research by his distinguished former tutor, Elinor; no one has ever discovered what she has been working on. Is that really possible?

Al is not all bad. Yes, he pushes for results, but he also exposes the scientific fraud being perpetrated by his bloodless colleague Christopher (a chilly, unrepentant Duncan Bell). Christopher holds a press conference to announce the discovery of the "sun battery". He has found the catalyst to create hydrogen out of sunlight and water. Why Christopher cheats - in an area where you will always get found out - is the central question of Poliakoff's play. The stranger question is why Al keeps mementoes of his life wrapped up like exhibits at a murder inquiry.

Hype, the desire for funding, the pressure for results: there are obvious reasons for the fraud. But there are other intriguing ones. In Ron Daniels' involving production, the different types of scientists are pinned down like laboratory specimens. Frances de la Tour powerfully evokes the loneliness of the long- distance researcher - a monastic life of Bach, bowls of custard, and romance on the lab carpet. Graham Crowden fruitily sketches in the cynical, clubbable emeritus professor, loftily abnegating responsibility as he slips into retirement.

It's Barbara (Hermione Norris), the research assistant, who betrays Christopher. But there's a strong suggestion that her memory is faulty. Did Barbara get it wrong? We never learn. Poliakoff slides one compelling theme after another under the microscope without letting us focus too precisely on the detail.

Five minutes into Yukio Ninagawa's fierce and beautiful production of A Midsummer Night's Dream, it looked as if this might be an ordeal. The cast perform in Japanese. There are no surtitles. There would be considerable emphasis on what we saw. What we saw were a few low-lying rocks scattered in the sand.

Thanks to a programme note we knew this represented a Japanese stone garden (symbol of the cosmos). The vertical columns of sand that fell down through shafts of light symbolise a forest, a spider's web and an hour-glass. I might have got the forest and the hour-glass. But the spider's web, no. When the very funny mechanicals play in front of the court they use slapstick elements from modern Kabuki theatre. Two actors play Puck. One does cartwheels, somersaults and backflips in the air. The other, annoyingly, stands at the side of the stage and speaks the lines. This is traditional in Noh drama.

You could learn about these directorial decisions from a five-minute slide-show. What makes Ninagawa's Japanese Dream worth seeing for Westerners is its clarity and vigour. The disputes between the lovers have a tough, elegant formality. Oberon and Titania have the harshest, bitterest quarrels I've seen. The mechanicals burst on riding bicycles, Bottom (Goro Daimon) cooks up noodles, and they create an electrifyingly self-absorbed hubbub. Ninagawa's Dream is full of passion, enchantment and - thankfully - visual humour. There's a very funny slow-motion sequence when Bottom returns to rehearsals wearing the ass's head.

Best of all, a former Sumo wrestler, Ofuji, plays Snug. He's head and shoulders taller than his colleagues and head and shoulders wider. In a lovely touch in the play-within-the-play, Snug takes off his mask to reassure the Court that he is not really a lion. Ofuji looks more frightening with the mask off than he does with the mask on. It's a Japanese joke that translates well.

The thriller Dial M for Murder returned to the West End (during the Edinburgh Festival) where it first ran in 1952. It could only be a period piece. This story of an ex-tennis pro who tries to murder his wealthy wife would never work if the wife lounged on the sofa of their flat in Maida Vale vetting her incoming calls on the answering machine.

Peter Wilson's surprisingly gripping production returns us to the Fifties world of sharply creased trousers, male chauvinism and dialogue that has to carry a lot of plot. The suspense techniques still quicken the pulse: the ring of the phone; someone's feet glimpsed by the light under the doorway; the latchkey jiggling in the lock; the figure silhouetted in the doorway.

Peter Davison is thoroughly convincing as the smooth-talking - if increasingly flustered - husband of the elegant Catherine Rabett. The cast - which also includes Brian Deacon as the naive crime TV writer, Peter Bourke as the Rattiganesque phoney Captain Lesgate, and John Vine as the decent Inspector - catch just the right sense of period. Vintage stuff.

Theatre details: Going Out, page 14.