Tilda Swinton (The Beach) plays Margaret Hall, a worried mother living in Lake Tahoe, Nevada with her children and her father-in-law. Her husband is in the Navy, currently stationed on a ship in the middle of the ocean, and therefore not available for contact. Margaret is greatly pained by her son Beau (Jonathan Tucker). A talented young high school musician, Beau has been hanging out with a club owner from the city. In the first scene, Margaret warns the guy to stay away from her son. She knows that this man is older but nonetheless engaging in a homosexual affair with Beau. She also knows that, during one of their contacts, they were in a drunk driving accident.

Despite her warning, the guy comes to the house in the middle of the night, has a fight with Beau, and ends up dead. The next morning, Margaret finds his body and, believing her son has murdered him, covers it up by dumping the body deep in the lake. It is a measure of the discord between mother and son that she is not able to ask him what happened, much less admit that she has disposed of the corpse.

A sympathetic blackmailer tries to help a troubled mother in The Deep End

Naturally, the body washes up and Margaret is soon visited by a blackmailer named Alek Spera (Goran Visnjic). He has a tape of Beau and the man having sexual relations. A threat is made: hand over $50,000 or the tape will end up in the hands of the local police department. The problem is that Margaret can't raise the money. She simply is in a bad position; her husband's gone, she has children who need to be taken care of, and her father-in-law is unable to help. Every desperate attempt at raising the cash comes up short. As the screws turn tighter, Margaret discovers that Alek is surprisingly sympathetic toward her. In fact, he seems as determined to help her as he does to blackmail her.

Their relationship is the heart of The Deep End. This is not a thriller about how the bad man died or whether the blackmailers will get their money, although both those questions are answered. Instead, the film explores the idea of this woman finding an unlikely ally in her moment of greatest need. Alek empathizes with the pinch Margaret finds herself in. He wants to help - not so much to get the money as because he is touched by her tenacity. He is the rare movie bad guy smart enough to see what's really going on and how someone can get messed up by a well-timed incident of blackmail.

That's a great idea for a movie, and The Deep End benefits from strong performances to back up the plot. Tilda Swinton is, as of this writing, my pick as the front-runner for the Best Actress Oscar. She portrays this woman as strong but crumbling, fierce but fragile, determined but lost. The character's life is a bundle of contradictions, which can be difficult for an actor to bring off. Swinton does it in one of the most remarkable performances you will see this year.

Visnjic ably backs her up, with his menace that melts into empathy. That's also a tough range to play but he pulls it off. The back-and-forth between the leads is fascinating stuff that gives the film an edgy excitement. Just as Margaret doesn't know what to do to raise the money, Alek doesn't know what to do about his assignment. Both people are stuck in a circumstance beyond their control; they are waiting for something to break in their favor. That similarity breeds a slow, steady bond as they negotiate their tenuous positions.

Directors Scott McGehee and David Siegel do a nice job grounding the story in reality. There is a quality here that is eerie without ever losing credibility. They keep the thriller aspects in line with the emotional and psychological arcs of the characters. You really believe this story could happen. You really believe that this woman would go to great lengths to protect her son. And, thanks to two superb performances, you really believe that a lowlife criminal could be the best friend a troubled woman could ever have.

( 1/2 out of four)

The Deep End is rated R for some violence and language, and for a strong sex scene. The running time is 1 hour and 39 minutes.