The first four seasons of True Blood were roughly based on books 1 through 4. The first season was fairly faithful to the book, although they did add some things like Jessica and Jason and Tara were minor characters in the book. The second season had the same basic story as the book (Sookie helps Vamps find Godric, but changed several things (the whole Maryanne storyline was not in the book.) The third season again had the basic story the same (Sookie and friends looking for a missing Bill), but changed some things (The whole Tara abduction by the vampire Franklin is not in the book. The fourth season is where the series begins to move away from the books. Bill is not the King of Mississippi, Sookie is not missing for a year from being in the Fairy world, and the vampires and werewolves join forces against a witch group led by Hallow. Eric does lose his memory though and has a relationship with Sookie and Sookie does kill Debbie Pelt, though Tara has nothing to do with it. So far this season has nothing to do with the 5th book.