Tilda checks out of the art house – and shows how good she really is

It never fails. Wait until the end of summer in America, and you have a chance of seeing a few good films, the ones the business thought not worth bothering with in the high season. This year's August sleeper for discerning moviegoers is The Deep End, written and directed by newcomers Scott McGehee and David Siegel. Don't be put off if I tell you that it's a movie about the virtue of mothers. It's also the breakthrough Tilda Swinton has been waiting for.

Or has she? I put it that way because, having had the pleasure of meeting her a few years ago, I treasure the sense of someone far more impressed by work, art and all the other things in life. The Deep End is actually a mainstream film that might easily have achieved bigger box-office. But Tilda Swinton has a history of doing things for their own sake, because they appealed to her, and because they came from friends undeterred by the question, "How can anyone that tall, that pale, with ginger-red hair, and so close to the look and spirit of the Pre-Raphaelites, hope to be the kind of glamour-puss movies now require?"

After all, Tilda Swinton's creative godfather was Derek Jarman. She had something to do in most of his films, and gave of herself fully and willingly without too much thought of payment or even expenses. She enjoys that kind of innocent comradeship, and she has renewed it with Sally Potter (for Orlando) and with the American experimental film-maker, Lynn Hershman (on Conceiving Ada and the forthcoming Teknolust). But in all of those films, she was an icon and a presence rather more than a mere actress, someone whose exceptional appearance was heightened for the particular roles and who was content to be an element in the artists' vision. It wasn't always obvious or possible to say from those pictures whether Tilda could act. That matter is now solved. She has won widespread praise for The Deep End, including a "magnificent" from The New York Times.

In a way, the success of The Deep End is not surprising. Over 50 years ago, the great Max Ophuls took the novel it's based on (by Elisabeth Sanxay Holding) and turned it into The Reckless Moment, which starred Joan Bennett and James Mason. In the new version, Swinton is the mother of three children, with a husband who's away in the Navy. She looks after the kids and an ailing father-in-law on the north shore of Lake Tahoe (a beautiful location admirably treated in the film). Her son is applying to college, but he's got involved with a gay scumbag in Reno. This man is killed in an accident on their lake-shore property, and just as she has to clean up after everyone in the family, so the mother has to dispose of the body. She manages, but then a blackmailer comes by. I won't go further into the plot, except to say that in the original, Mason played the blackmailer – so you know the story has only just begun.

It's part of the actress's success that no one in America, I suspect, is going to detect Swinton's Scots and military parentage, much less her schooling with Princess Diana. She sounds American, and she feels like the kind of uncomplaining woman who might live in Tahoe City (a resort town in summer and ski season, but not really a place to reside), looking after a demanding family while her husband plays battleships. You believe in her utterly when she says she could never admit to the husband that their son might be gay. You can also credit that she is strong and determined enough to get a corpse in and out of a motor boat and dump it in the lake (the last movie character who went into that cold, clear water was Fredo Corleone). Swinton even swims in the lake – which, I have to tell you, takes resolution.

The reason why The Deep End works is because a noirish melodrama has been imposed skilfully on a real, untidy family situation. But without success. The family realities keep breaking through, and there are several occasions where criminal need compels Swinton's character to do one thing while sheer family imperatives are shouting "Me! Me! Me!" Swinton recently became the mother of twins. Here on screen, she has three children with quite different needs. Indeed, she's playing a woman whose own life has been squeezed flat – until very special circumstances bring her back to her self. In the way of the movie world, The Deep End may be forgotten by next Oscar season, but if we see a better performance this year by an actress, we'll be lucky.

David Thomsond.thomson@independent.co.uk

'The Deep End' is released on 2 November