Grade: B

Scott McGehee and David Siegel, the duo behind the pleasingly oddball “Suture” (1993), have gone a similar route with their second feature, but the results are more inconclusive. The earlier picture posed as a thriller about a man, suspected of killing his father, who plots to fake his own death by substituting the body of his estranged half-brother for his own; but though the half-siblings constantly remark on their physical likeness, one is white and the other black, and they look nothing alike. The whole device was a joke, of course, which invited the audience to ruminate on the nature of identity, and although it wasn’t entirely successful, it provided a good deal of fun. Now they’ve adapted Elisabeth Holding’s near-forgotten 1947 novel “The Blank Wall,” about a woman who tries to cover up the death of a fellow who’s seduced her daughter, only to find herself hounded by a blackmailer. The book was already the basis for a sturdy noirish melodrama, “The Reckless Moment,” made by Max Ophuls in 1949 with Joan Bennett and James Mason. But McGehee and Siegel don’t attempt a straight, period recreation of the narrative; they update it to the present, set it along the scenic shore of Lake Tahoe, and alter the story by having the mother dispose of the corpse of a homosexual man whom she believes was done in by her son, a promising young music student who’s discovering his sexuality. But she still becomes the target of a mysterious man who’s rather conflicted about his actions.

The outcome of all this tinkering, “The Deep End,” is a mixed bag. Stylistically it’s quite remarkable, as “Suture” was; shot in crisp, widescreen color, it often has a stunning look. The visual metaphor that it utilizes, quite brilliantly, is that of water. There are many shots of the rippling lakeshore, of course, and a quite remarkable scene in which the heroine, Margaret Hall (Tilda Swinton) has to dive into the lake to retrieve a set of keys that she’d deposited there with the dead man’s body. (The sequence is a bit reminiscent of the unforgettably dreamlike moment in Charles Laughton’s 1955 “The Night of the Hunter,” in which we see the murdered Willa Harper–the young Shelley Winters–sitting in an old touring-car at the bottom of the Ohio River.) Many moments are shot, moreover, through a large aquarium in the Halls’ wood-paneled living room, and one image of Margaret entering her kitchen is even filmed through a drop slowly squeezing out of the faucet of a sink. The effect is to tell us that we’re observing the action almost clinically, as though we were viewing fish swimming about in a bowl, and that there are unexpected things churning below the surface of placid everyday life.

When we come to the mechanics of the plot, unfortunately, it quickly becomes clear that the specifics of Holding’s creaky 1940s contraption no longer–if you’ll pardon the pun–hold water. As a thriller “The Deep End” is simply preposterous: the conventions its makers have retained from the original seem absurd, and the alterations they’ve made to increase the plausibility aren’t much better. The entire crux of the death-and-blackmail scheme is based on a series of ridiculous coincidences than even a stylish surface can’t gloss over; and later, the blackmailer just happens to arrive at the house at the very moment that Margaret’s father-in-law is suffering a life-threatening heart attack. Even the blackmail business itself isn’t credible: it’s hard to believe that a hard-as-nails Reno dude would bother trying to hit up a middle-class housewife for $50,000, or that the mysterious man who approaches the woman (here played by Goran Visnjic) would turn so soft and sentimental that he’d sacrifice his half of the take, let alone his life, to help her save her family.

But if you forego literal plausibility and instead take “The Deep End” as a surrealistic, almost nightmarish depiction of the life of a harried single mom, it’s rather an enjoyable ride. Such a reading lends a streak of morbid humor to moments such as when Margaret has to change a date with the blackmailer because she has to pick up the kids, or is unable to get a bank loan because her husband isn’t there to cosign, or is forced to hire a taxi for a rendezvous because her car’s on the fritz. These kinds of grace notes make the whole thing palatable, and even in a way touching.

The performances help, too. The men–Visnjic, Jonathan Tucker as Margaret’s troubled son Beau, and Peter Donat as her father-in-law–are all sound, but it’s Swinton’s overpowering turn in the lead that energizes the movie. She doesn’t push too hard; indeed, it’s the mousy, recessive quality she brings to the part that makes her portrayal so affecting and effective. But she also captures the inexhaustible reservoirs of strength beneath the woman’s quiet, often nervous exterior. You get the feeling that this is a mother who would do literally anything to defend her brood.

Swinton’s masterful portrayal, the clever subtext and the stylistic flourishes that McGehee and Siegel bring to the proceedings help “The Deep End” overcome its serious deficiencies as a thriller and become an intriguing, if flawed, picture of a woman driven to the most extreme measures to protect her wayward son. In a case like this, one should not allow one’s desire for the perfect to become the enemy of the good.