In London at the moment, one of the things that the tabloid newspapers get themselves worked up about is the fact that Russian, Bulgarians and various other Eastern Europeans are being transported over here to work as sex slaves by the Russian Mafia (which is also called Vor apparently). This film plays on that idea, with Mortensen playing a "Vor heavy" in London who is trying to muscle his way to the top, and Watts the nurse who accidentally stumbles on the "Vor" when her character (a nurse) aids in an operation that sees a young heroin addicted prostitute die after her daughter is born.
It's probably one of my favorite films of this year (despite some obvious flaws -the "crack baby" is extremely well behaved for example), but don't expect it to be an uplifting film. It isn't. The film has a "happy ending" of sorts, but even that could better be described as a "lesser of several evils" ending.