Martin shows up on Blomkvist's doorstep with the latest edition of the Hedestad Courier, which features a scathing article suggesting that Blomkvist's presence in Hedestad is a problem for the community. Martin insists he had nothing to do with the article and that he's willing to write a response expressing his disdain at such biased reporting. Blomkvist takes this news calmly, not seeing the article as much of a threat as Martin makes it out to be. Martin uses this opportunity to repeat his suggestion that Blomkvist return to Millennium and again Blomkvist refuses, indicating he and Salander have made some progress toward solving the Harriet mystery.
Later on, Salander and Blomkvist review Mildred's photo, using his computer to sharpen and tighten the image of the mysterious figure. At best, they're able to see that person is likely a man, but the features are still obscure. Salander and Blomkvist settle into a comfortable routine allowing them to work and live together in peace. Eventually, Salander suggests they investigate arson and animal mutilation cases near the times of the murders as often serial killers have a history of these horrid acts, sometimes in their youth, before they become murderers.
After a few days, Salander realizes that, for the first time in her life, she is sharing her living space with someone, and that other person isn't even driving her insane. She also realizes that she desires Blomkvist and, late one night, enters his bedroom and seduces him. They wake up, both in happy moods, until they see what awaits them outside: Tjorven, the neighborhood cat, has been brutally killed and its severed head rests on the seat of Salander's motorcycle.
Salander and Blomkvist's investigation takes a sinister turn in Chapter 21, as characterized by Blomkvist's interactions with Martin as well as the brutal slaughter of the cat, Tjorven. First, Blomkvist and Martin once again have a mild confrontation regarding Blomkvist's return to Millennium. While Martin insists that he supports Blomkvist's decision, Martin continues to suggest reasons Blomkvist should go. Martin uses evidence in the form of the Hedestad Courier report to more firmly push Blomkvist out of Hedestad. This scene builds on the prior confrontations between these characters and indicates that neither, despite his outward politeness to the other, is ready to back down. Martin's motives for having Blomkvist return to Stockholm also are called into question..
Secondly, the death of Tjorven acts as a vicious warning to Salander and Blomkvist on a variety of levels. First, the gross violence present in the killing of the cat mirrors the violence Salander and Blomkvist have been researching on the women's murders. Like at least one of the women, the cat has been decapitated. Additionally, Tjorven's death brings animal mutilation literally to their doorstep. No longer is the cruelty simply something they're researching to find a killer, the animal torture is a signal that the killer knows Salander and Blomkvist are on to something. Finally, because Tjorven has been present as a symbol of hope and comfort for Blomkvist, her death indicates that hope will be difficult to find as Salander and Blomkvist continue their quest.