The story is an interesting web of inter twined stories but the main story is about a journalist (Michael Blomkvist) who is, after having gone through a jail sentence, officially hired to write the family story about a powerful family. He is hired by the old head of the family and he has another motive for hiring him. He gets help from a young women (Lisbeth Salander) who has gone trough a lot and is considered psychopathic and sick. But she is also a genius as a researcher and hacker.
The story deals with multiple storylines presenting both Michael and Lisbeth and a main story with lots of twists and bends that keeps you guessing until the end.
One of the best books I have ever read. I freakin' love it. Characters are unforgettable and so new, not anything like in other books. I highly recommend this book.