Opens Fri Aug 17 at Harvard Exit.

Though it comes dressed in the icy blue clothes of a suspense thriller, The Deep End is a far more interesting creature. Using its intricate plot as shrewd camouflage, the film serves as an examination of the evolving relationship between a lonely mother and her gifted teenage son, whose sexuality (homo) is such an impenetrable subject that Mom (the ineffable Tilda Swinton) would rather navigate a murder cover-up, blackmail, and death threats than talk to the lad directly.

Set in the isolated vastness of the mountains near Lake Tahoe, the story begins like an old-school film noir. Soccer mom Margaret (Swinton) goes to a gay bar (called the Deep End, bathed in warbly blue swimming-pool light to match) and warns Darby, the bar's shady owner, to stay away from her son, Beau. It's clear that Margaret is uncomfortable, but that her maternal instincts prevail over her squeamishness--a fact reinforced soon after, when she discovers Darby's body, impaled by an anchor beside a dock behind her house.

The killing was accidental, following a tussle between the older man--a manipulative chicken hawk--and his young quarry; so accidental that Beau doesn't even realize Darby is dead. Margaret, after a moment of panic, takes the situation in hand and rows out into the lake to dispose of the corpse, returning home to her now-officially dysfunctional family.

Throughout the rest of the film, Margaret and Beau purposefully avoid confrontation, each assuming the other knows more or less than what is being said--a beautiful distillation of the ties severed by adolescence. Throw in a hunky extortionist (Goran Visnjic) with a very private videotape linking Beau and Darby, and you have the ingredients of a deceptively engrossing potboiler, where the plot takes many an engrossing, implausible turn, but the real action takes place in the lead character's mind.