The Girl With The Dragon Tattoo is the first in the Millenium series by author Stieg Larsson. Having lost a libel case journalist Mikael Blomkvist is hired by Henrik Vanger to look into the disappearance of his granddaughter Harriet Vanger forty years ago. During the investigation Mikael realizes he needs a researcher and so employs Lisbeth Salander to assist him.
It is at the same time both hard and easy to see why the book became an international bestseller and so popular. Hard because the subject matter can be particularly sexually violent at times and there is a graphic rape scene.