Survivor Chronicles 3 Shepherds and Wolves:

Andre, the betrayer makes his way through the sewers of Jefferson as two armies fighter overhead. There he finds one surprise after another as his plans fall apart. To the west a vast army of crusading pilgrims is on the march, straight towards Haley and Jason. Devouring any and all who come into their path, as they wage war on the remnants of humanity, and to bring our species to a fiery end at last. Third book of the series.