In this chapter, we learn that aelric is using the power of the "spirit of shadow" to control the vampire population in the north of England. This means that if a vampire kills a human, the vampire will no longer be able to use the "power of spirit" to gain control over the human population. In other words, if the vampire kills one human and then kills another, that vampire's power of spirit will not be restored. This is because the vampire is still a "blood lust" vampire, and killing a human is not a good way to kill a vampire. In fact, the only way to stop a vampire from killing another human is to kill the vampire first. The only way for a vampire to kill another vampire is by killing the human first, and that's what aelfric is doing. He's already done that, and he's not going to stop until he kills the vampire who's trying to kill him.