What do the vampires do to start the fight between themselves and Harry's group?

Bianca presents Harry with a tombstone at the gift-giving ceremony. Lea then steps forward to present Bianca with Amoracchius. Lydia is brought out, and Mavra steps forward, intending to kill Lydia with Amoracchius, thereby unmaking the weapon. Michael and Harry decide that they must do something to save Lydia, and keep Amoracchius out of the wrong hands.