I'm confused, whats the werewolf angle? (spoilers)

the guy got bit, the girl in the volkswage dead, there's something in a locked room with the bad vampires, there are good vampires, I don't know who is who, can someone sort this all out?

how and why did the guy get bit? am I supposed to believe that its a coincedence that the guy with the last amulet accidentally comes across the girl in volkswagen and gets bit, but then doesn't get killed (why?)