The writing team came up with a somewhat stilted gimmick fort his novel. The Witch Oracle has been looking into Kate's future more or less since she claimed Atlanta and they do _not_ like what they are seeing, not one teeny tiny bit. They tell Kate and Kate doesn't like it either. So she starts thinking outside the box and opens up some possibilities; it turns into one of those scavenger hunt/serial murder or criminal leaves a bunch of puzzles for the heroes to solve episodes. In 70s era crime drama, it involved payphones; in this case, it involves confusing checkins with the Witch Oracle.
On the one hand, this could really be silly and annoying. On the other hand, it works fairly well as a Kate Life Review. Each of the anchor points involves Kate revisiting a friend or family member, and the past is reinterpreted (sometimes very tragically, sometimes in a way that leads to some optimism). Kate's relationships with her close friends are strengthened and by the time the final battle arrives, I doubt anyone is particularly surprised to learn that every single one of the anchor points preserved the life of a friend whose contribution to the battle is crucial (or, in at least one case, precipitated a death that was important, or, yeah, whatever).
Neat book. I love who Kate and Curran picked to officiate; it is in every way appropriate. And I'm looking forward to more in the series and the universe.