By OnMilwaukee Staff Writers   Published Aug 21, 2001 at 4:42 AM

Being a mom isn't easy, especially for Margaret Hall (Tilda Swinton) who must raise her three children alone while her husband is away on a Navy aircraft carrier. Hall and her kids live near Lake Tahoe with her father-in-law. As if the day-to-day responsibilities weren't enough, she discovers that her teenage son Beau (Jonathan Tucker) may have killed a man.

"The Deep End" shows just how far a mother will go to protect her child. It's an involving and suspenseful film, but the highlight is Giles Nuttgens' astonishing cinematography, which makes this one of the most aesthetically pleasing films in years.

Beau has gotten involved with an older man named Darby Reese (Josh Lucas). Darby owns a nightclub, drives a fancy sports car and seduced the innocent Beau. Margaret knows this and tells Darby to stay away from her son.

The relationship between Margaret and Beau is a fragile one. She is concerned about him but he wants to be left alone and they have heated arguments.

Late one night, Darby comes over and convinces Beau to sneak out of the house. They go to the boathouse on the lake and fool around a little. But abruptly they get into a fight and Darby becomes violent. Beau runs off and heads back towards the house.

The next morning, Margaret finds Darby's body near their dock. He fell off of it somehow and landed on a spear.

Her maternal instincts kick in immediately. She wraps up the body and loads it into a small motorboat. She drives to a secluded area, checks to make sure that no one is around, and then dumps the body into the lake.

Back at home, it's business as usual. Taking the kids to school and getting groceries and all that good stuff. Of course, the trouble is far from over. First of all, Margaret has some questions for Beau. Did he kill Darby? What exactly happened that night? Will the police want to question him?

To make matters worse, a mysterious stranger named Alek (Goran Visnjic) arrives, demanding $50,000. He happens to have a videotape of Beau and Darby having sex. The money will buy her the tape. Either she pays or he mails it to the police.

Written and directed by Scott McGehee and David Siegel, "The Deep End" is an interesting thriller with a few tricks up its sleeve. It doesn't go where you initially expect it to and features a convincing and powerful performance from Swinton ("The Beach").

The movie also contains two nicely developed relationships: one between Margaret and Beau and the other between her and Alek. The former is entirely believable and often moving, while the latter is complex and full of sexual tension. Both are masterfully portrayed.

The conclusion is a bit of a letdown, if only because thus far the movie has built great suspense and attempts to remain as realistic as possible. The disappointing ending goes a little overboard and strains credibility.

But up until that point, "The Deep End" is an engrossing ride. If nothing else, it's worth the price of admission just for the scenery. This is a sumptuous movie.

Grade: B+

"The Deep End" starts Wed., Aug. 22 at Landmark's Downer Theatre. Click here for showtimes.