Sci fi book need to know title

[Willellison13]

I'm searching for a science fiction book I read a while back it starts off with some sort of detective bounty hunter or police officer on earth who leaves for a planet that is mostly blue to investigate a city that has started to build itself there is also a race of humanoid aliens on the planet one of which who he has a romantic encounter with an end up fighting her husband

 

[Willellison13]

The alien described seemed alot like the one from avatar and I believe some sort of war or conflict was also being waged at the time, I belive this book may be part of a series and the guy main character could also mimic faces