I spoke before about The Girl With the Dragon Tattoo. I've not read the other books in the series, but apparently some of them involve the crime of human trafficking.
The books take place in Sweden. It's not uncommon to hear of these crimes in other parts of the world. We forget that the United States also has a problem with the grotesque crime of trafficking. There is an interesting piece in the NYTimes on this subject.
The book was hard for me to get through...but there are some things we, as humans, need to be aware of. Crimes that other humans commit all too easily. If these books shed light on such crimes, then I'm glad they're on the bestseller lists.