The dress rehearsal has just finished; tomorrow we start the previews of Mindgame in front of a paying audience. Warhol's muse Sylvia Miles, of Midnight Cowboy, and Pamela Marvin, the widow of Lee Marvin, are coming. Do we need to change the line in the play, “Lee Marvin was killed in Stanley Donen's Charade”? Don't want to upset the lady.

That's the least of our worries. How can we have a curtain-up if we have only half a curtain? My stalwart crew assures me that they will work all night if necessary to get the remainder up and in working order for tomorrow.

Apart from that, all is going well, even tricky bits - from the brutal stabbing of Nurse Plimpton (Kathleen McNenney) with three types of fake blood, permanent, washable and edible, to the ever-shrinking psychiatrist's study designed by the crafty genius of Beowulf Boritt.

This shrinking scenery, linked to an intricate series of wires and gears offstage, is masterminded by Eric Parillo, the understudy. There is a giant wheel in the wings, which he turns slowly every eight minutes throughout the show. We have all heard of Chinese water torture. Well, this must be the Mindgame torture.

Over the past two weeks of rehearsals we've slowly incorporated fresh business and rejected almost as much again. Giving the journalist (Lee Godart) a snazzy automatic to shoot his way out of the asylum with blanks has gone, as has the massed manic laughter of the lunatics every time a door is opened. The hairnet-over-hairpins look for Nurse Plimpton is out. Gone is the star Keith Carradine's golf suit, though a single club remains - sinister. Gone is the amplified sound of a homicidal maniac driving over dear old dad, then reversing over him just to make sure. Instead, the conversation refers to the torrid tale sans sound effects - funnier.

Added - a baby skeleton in the fireplace, incidental music from Delius and Stravinsky, vents in the straitjacket (thick as rhinoceros hide) to keep Lee from suffocating under the lights. A resounding slap is rehearsed over and over.

After a fortnight of directing complete run-throughs of the same sinister story, sometimes twice a day, I am ready to answer the question of whether I have a preference for directing for the stage or the screen. I am also ready to recite in my sleep 111 pages of text, but that's merely a side effect of repeated viewing.

To tell the truth, both stage directing and film directing have their pluses and minuses.

For the stage, you have the bonus of rehearsing the story as it happens, from revelation to reversals to conclusion, whereas in movies you have to make an inspired guess as to how your characters would behave in any given moment. This is because, for reasons of finance, films are generally shot out of sequence. If all the scenes were shot in order, a film unit of 60 technicians would be dashing off to a different location every day at great expense, whereas if the entire unit stays put until like scenes are completed, it certainly helps the budget.

With a stage play, you can change your mind right up to the first night. But at least with films you don't have to suffer the boredom of endless run-throughs. On the stage a director sits through every last word every livelong day for a month, by which time you can be close to script schizophrenia. I can only imagine what the actors go through, permeating themselves with the language and actions till their original self is erased for the run of the play.

But that's the nature of the beast. Under the lights and in person, the acting takes on a luminosity and visceral attraction, like a ritual ceremony or magic act. And there's always something to monitor in addition to the actors: the ever-moving set, the props, the sound, costumes, lighting - even the pre-publicity, with endless newspaper, magazine, radio and TV interviews. As the previews approach, the rehearsal time stretches from noon to midnight - very unlike the eight-hour day in the film industry. Off-Broadway shows seem a law unto themselves, where even understudies (including Amanda Barron, from Southampton) double up as assistant fight directors and fire marshals.

First preview and the curtain's finally in place. But it's too long and bulky and bunches up when fully open, hiding a substantial part of the set. Quick revamp of business that takes place downstage too near its voluminous folds. Worse still, the picture on the wall, which gradually morphs from a man to a woman, refuses to co-operate. Disaster! May have to drop it because of the exorbitant cost of TV and DVD equipment. For, as I am constantly reminded, off-Broadway productions work to very tight budgets. Having spent a substantial amount on a beautiful backdrop of a sunlit English country garden, there's not enough money left in the budget to hire the necessary lamps to illuminate it. Instead of a bright summer's day, it looks more like a twilight summer's evening.

Ever resourceful, I change Lee's spoken diary entry from “5.15, July 21, at Fairfields Lunatic Asylum” to “9.15, July 21, etc.” I hope the author, Anthony Horowitz, doesn't take umbrage. I doubt it, since he has already offered to change key words as a concession to our American audience and is much relieved that I've refused. The lunatic asylum will still be set near Colchester in Suffolk, not in the Bellevue of East Manhattan. Serial killers such as the Wests and Myra Hindley feature, not Son of Sam or the Boston Strangler. There's Jeremy Paxman, not Tom Brokaw; and the M25 is not the interstate. The murders all take place in York, not New York. Mindgame is still as British as the flag. And that goes for the impeccable English accents of the impeccable all-American cast.

Guess I'm kinda a lucky guy, ya know?

Mindgame is at the SoHo Playhouse, 15 Van Dam Street (btw 6th Ave & Varick), NYC. For tickets: 001 212 691 1555 or Mindgametheplay.com

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