Final answer:
The second book in Stieg Larsson's Millennium trilogy is 'The Girl Who Played with Fire,' which delves deeper into Lisbeth Salander's past.
Step-by-step explanation:
The second book in Stieg Larsson's Millennium series is The Girl Who Played with Fire. This novel continues the story of Lisbeth Salander, a skilled hacker and investigator, and Mikael Blomkvist, a journalist. In "The Girl Who Played with Fire," Salander and Blomkvist become involved in a case dealing with sex trafficking and governmental corruption, which leads to a deeper development of Salander's dark past and character.