Per my review at Baltimore Reads: 
 Considering this is the first book in the Millennium series, Larsson is tasked with introducing his central characters to readers. After a mysterious opening featuring an old man haunted by an anonymous gift of a framed flower on his birthday, readers meet journalist Mikael Blomkvist, who has just been found guilty of libel against a big-shot businessman. For a suspense novel, The Girl with the Dragon Tattoo has quite the slow start, stock full of business jargon that may go over some readers' heads (as it did mine). But don't lose heart; it isn't essential to understand the ins and outs of the crooked dealings of Hans-Erik Wennerstrom. What is important to realize is that Blomkvist, while he accepted his sentence, still believes Wennerstrom to be corrupt but now has to do his best to put his career back together and save his magazine, Millennium, from a disastrous collapse. 
 Meanwhile, the series' other main character, Lisbeth Salander, is working as an investigator for Milton Security. The tiny, tattooed, socially inept Salander is a wiz at digging up even the most private of facts about individuals, much to boss Dragan Armansky's amazement, but in all other areas of life she is hopelessly unpredictable. She does what she wants, when she wants to, and answers to nobody but herself, which has prompted the government to declare her legally incompetent. Despite her hardnosed independence, she has earned the respect of Armansky and her guardian, Holger Palmgren. Her life takes an unfortunate turn when Palmgrem suffers from a stroke and is replaced as guardian by Nils Bjurman, who uses his authority over Salander in the worst possible way. 
 The two protagonists' worlds don't collide until over halfway through the novel. Blomkvist, who is delving into the past of the Vanger family in search of answers about the disappearance of a young girl (under the commission of Henrik Vanger himself), has isolated himself in the Swedish town of Hedested. His incentive to solve the case is rooted in Vanger's promise of damning evidence against Wennerstrom. Yet Blomkvist finds himself in a bind and needs help from an outside source. In comes Salander, fresh off a harrowing secret war with Bjurman, and what transpires is a riveting and suspenseful chain of events that leads to the chilling basement of a sadistic murderer. 
 The Girl with the Dragon Tattoo provides an adequate introduction to Blomkvist and Salander, who combine to make an almost unstoppable team. Readers come to know their personalities, their strengths and weaknesses, their triumphs and mistakes. Blomkvist is a loyal and honorable journalist, but his devotion comes to a point that is sometimes reckless. He is also quick to jump in bed with any woman that expresses interest. Salander is incredibly gifted and smart, but her tendency to want to shoulder everything on her own is extremely unhealthy. She is a petite girl who is anything but helpless - in fact, she kicks major butt. She is also anything but a prude, which makes it difficult for her partnership with Blomkvist to remain simply business. This first novel ends with the two at a crossroads. The plot comes to a definitive end, but Salander's and Blomkvist's storylines are only just beginning.