Find shelter or die.
Travis Hunter is in Manhattan when the earthquake hit, and finds himself running towards whatever safety he can get to. Afterwards, the survivors gather to make some sense out of what just happened. Shortly afterwards, Hunter finds himself released only to be contacted by a Higher Power to take up a mission as a Runner. Informed that it is now his job to lay down judgement upon all the remaining humans, Hunter takes off to circle the world with Encautum, completing the circle to finish his mission.
While Hunter attempts to stop and help folks on his trip, it seemed like he was given very little choice in his actions. Mostly, he just walked (flew, hopped, etc) around the world, only to be confronted back where he started by a group of survivors. This left a lot of questions to be answered, hopefully by the rest of the books in the series.
A quick post-apocalyptic read, As Darkness Ends sets up the other viewpoints to come in the series by giving us a different take on the end of the world.