The Alpha and Omega mated in the initial chapters of the series when they realized that they were the best for each other. They enhanced their powers and clan after their mating and now they have the duty to protect the werewolves wherever they exist. They have faced demons, vampires, and even humans who have tried to attack the werewolves.
In the Northern California Mountains, an entire town gets vanishes. This is where the FBI closes the case too because the department fails to find any kind of clue associated with the town. The owner of Aspen Creek is given the duty to solve the case on his own and he too thinks that the people have left on their own because of an unknown reason that they didn’t want to talk about. The pack of wolves living close to the area also had certain people in the town to whom they were connected.
So when the wolves get worried, this is where Charles and Anna come to the surface. Patricia Briggs has presented Charles and Anna as enforcers in the series. The two are not going to enforce anything on this occasion because the thing which has awoken in the forest is out of their control.
Holter Graham existed in the narration during Alpha and Omega and Night Broken so there was no chance that he would not be selected for this installment of the series. Darkness is haunting the entire community and something has to be done by the alpha and omega or it will spread in the entire world within time. There are people in the community who know more than they are telling Charles and this is another issue that gets them linked to grave problems.