While vengeance is the main focus of the story it is only part of the tale. For Raub that is all he sees. Darcy assumed he was dead yet the Lovack's alien metabolism keynote him alive. Healed and augmented along with a brainwashed and augmented Adam, Raub plans his revenge.
Forced to fight her boyfriend as well as the mad alien hunter, the ending fight was a bit anti-climactic. While she bears Raub yet again she does not kill him... That is done by Raub's own sister. Adam brainwashed, confused and no longer fully human leaves her to find his own peace.
While this nicely wraps up book 3, Inheritance, I don't see how either off them add to the story. Hopefully book 6 will bring it all together as promised.