The Morning After - The Enemy Within - Jason B. Kruse - Bog

In this continuation of the Morning After series, it has been a year since the world became infected by the deadly virus that killed and reanimated 90 percent of the human population. We find that Jacob, Jennifer, and the rest of our survivors have reached the outpost of California, as the war against the dead continues. Jacob and the alliance, a coalition of alien worlds, assist the human survivors in the fight to eradicate the dead.
While returning from a mission, Jacob, with the remnants of the human military, discovers a sinister plot set against the alliance and the people of Earth. An ancient rival, which thought destroyed a million years ago, has surfaced on Earth, placing the remaining population and all worlds within the alliance in jeopardy.
Now Jacob and his soldiers must act before what has befallen Earth is repeated throughout the galaxy.