Sovereign:

Sovereign The Book of Mortals- Book #3 By: Ted Dekker and Tosca Lee
Fiction: Sci fi/Fantasy, religion, 327 pages
Book Count: 35

The review of the second book in the series can be found here. This book is the ending of the series. 

The book picks up years after book two.  There are only a few Mortals left and they are being hunted by both the Dark Bloods and the Immortals.  Then one of them make a virus that will kill both the Dark Bloods and the Immortals, the only down side is that it could turn them back to what they were before they ever encountered Johnathan. The scientist will not listen to anyone that points out that that will destroy them too, and is going to release the virus no matter what.  Rom runs to Feyn to try to save her and Jordin runs to the desert to find Roland and save the Immortals.