River Marked is the sixth book in the Mercy Thompson series. I always end up with sleep deprivation while reading a Briggs novel but it's worth it. In this book Mercy and Adam finally get married. That's just the beginning of this story though. The real fireworks start on their honeymoon.
It turns out that the fae have steered Mercy and Adam to a lovely campground on the Columbia River for their honeymoon. The fae always have an ulterior motive and the river is the key. Unfortunately werewolves can't swim so Mercy is on her own. This book has plenty of action, and fascinating but deadly creatures. You'll be surprised at who turns up from Mercy's past that nobody was expecting. Very highly recommended.