In Eclipse, the werewolf pack grows to ten members. During the bonfire in La Push, we learn about werewolf history and their age-old hostility toward vampires. Jacob introduces Bella to the strange quirk of imprinting – a "love at first sight" for werewolves. Two of Jacob's werewolf friends imprint on their partners for life: Jared imprints on Kim, and Quil imprints on Claire, a two-year-old girl. When Bella expresses her shock over this constellation, Jacob tells her that Quill is designed for Claire. He'll be what she needs him to be as she grows up.
Two new additions to the pack also figure prominently in the story: Leah and Seth. Leah is Sam's ex-flame, and becomes the first she-werewolf to join the pack. She's still bitter about Sam choosing Emily over her, although she knows that imprinting left him no choice. During the battle with the newborns, Leah takes on a vampire to prove herself and Jacob almost gets killed in saving her. Seth, on the other hand, earns his stripes in battle when he and Edward finish off Victoria and Reilly.