Screenwriter Steve Knight presents Eastern Promises as a sister piece to his script for Dirty Pretty Things -- both are about immigrants who made their way to London looking for opportunities, only to become trapped in the city's seedy underworld. In Dirty Pretty Things, they had to deal with the black market for human organs; in this one, they fall in with the local Russian mafia, an organization known as the Vory V Zakone. Knight seems to see his stories as an exposé on the side of London we don't hear about, but they also border on that exploitative feeling of being trashy and unsubtle.

Director David Cronenberg, therefore, does the best favor for Eastern Promises by making the atmosphere serious and heavy, with its gruesome criminal dealings stark and its potential romanticism countered by vivid brutality and cold blood. Also, the parts that may have been titillating -- in particular, a scene where gangsters played by Viggo Mortensen and Vincent Cassel make use of their organization's sex slaves -- are drained of tawdriness until all that's left is, appropriately, disturbing sadness. Cronenberg is more interested in presenting this world at its face value, in all its violence and degradation.

And, as Cronenberg's primary vehicle, Mortensen  makes the show his own. The movie starts with Naomi Watts as a midwife, Anna, who delivers a baby whose mother, obviously abused, dies in childbirth; later, Anna's search for the baby's family leads her to a restaurant which serves as the front for the Russian mafia, all headed by the duplicitous Semyon (Armin Mueller-Stahl). Mortensen appears as Nikolai, a driver for Semyon's son Kirill (Cassel). As the movie goes on, this seemingly side character becomes more and more the focus -- his calm nerve and confident authority contrasting and at times overshadowing Kirill's flagrant recklessness.

Mortensen plays the character so strongly the movie stops being about anything or anyone else. The more we get to know him, the denser his mystery gets. His experiences soon embody the harsh truths of being a part of this underworld. It culminates in what is sure to become the most talked about scene in the film -- a hand-to-knife-in-hand struggle in a Turkish bathhouse. Mortensen foregoes bodily modesty in a raw fight scene that literally lays bare this subculture's history of violence.

Mortensen is the reason to watch this movie, and while his co-stars all perform admirably, the business about the baby all gradually falls by the wayside (though Cassel does get to have one very effective redeeming scene involving said baby) and the script's built-in concerns about mistreated Russian immigrants start feeling perfunctory. Cronenberg applies his strengths to the characterization of Nikolai, who  effectively steals all of the film's gravity. The central performance is thankfully strong enough to survive what I consider the pin that bursts the bubble, a story turn that occurs at the end and takes away the movie's juicy moral ambiguities. Up to that point, I was held in its thrall; afterwards I lamented how so many shades of grey suddenly became as clear as black and white. A little time away has allowed me to appreciate the grey  that remains as well as to further admire Cronenberg's technique and Mortensen's intensity.

(Released by Focus Features and rated "R" for strong brutal and bloody violence, some graphic sexuality, language and nudity.)

Review also posted at www.windowtothemovies.com.