The 36-year-old mystery of Harriet Vanger makes The Girl With the Dragon Tattoo seem like one gigantic cold case. Blomkvist and Salander journey deep in Vanger family history, struggling, like the readers, to pick out the important suspects. In the process, they discover very present and very horrific crimes. Tattoo seems to make an argument about history: studying it is important, and can help us make the present a safer and more just place. Tattoo also sets us up for a journey into Salander's past in the next two books. Apparently, she has some dark memories the narrator doesn't share with us.