Firstly, this is probably one of the best ends to a series that I have read. 
 Darkest Mercy is full of turmoil, loss, betrayal, intense emotions, undeniable love and change; with the whole series leading to this action filled climax. 
 Keenan, the Summer King, is missing. Wondering for the last six months trying to secure allies for the war he knows is coming. But while he has been absent the rest of the Faery Courts have been falling apart. 
 Aislinns had to take the reigns of the Summer Court fully in her hands, while Donia tries to bury her feelings for Keenan and make an uneasy alliance with her. The veil to Faerie has been sealed, unbalancing the Dark King Niall, and with Irial on his deathbed he becomes more unstable, and violent. Seth returns from Faerie seeing far too many threads, too many possibilities, and too many of them disastrous. Bananach grows stronger every minute and Death haunts the streets. The question is: Who will survive the coming battle and who will fall? 
 Darkest Mercy was a fantastic end to the Wicked Lovely series. It's been a while since I have read the previous books but I was able to jump right back into the story with ease. Despite being over 300 pages I flew through this in less then a day. I smiled, I got teary eyed and I was sad when it ended but it was a good, satisfying sad. 
 Melissa Marr does not make it easy for her characters to achieve their own HEA's. Each one is put to the test, their limits pushed, their body and hearts battered. 
 Keenan has always been one of my favorite characters and he really grows in this final installment and the changes he goes through for his court, his queen and his love is inspiring. Ash on the other hand, I found to be a bit weak, though she did finally put on her big girl panties towards the end. Both Nial and Irial remain dark and intense with their, sometimes unwanted, bond strong while Donia is pure strength and Seth logic. Those in Faerie do not play that big of a role in this last book and Leslie makes some important cameos but this is really about the four main courts and tying everything together. The crazy twists Marr throws keeps you guessing, every time I thought the story was going to go one way it took a totally different direction. She fearlessly takes you on a dark ride that is both tragic and lovely. 
 I will say that you need to read the previous books in the series to understand what is going on in Darkest Mercy. Otherwise you will be lost. Darkest Mercy is up to par with Wicked Lovely and definitely outshines Radiant Shadows and Fragile Eternity. 
 There are still a few unanswered questions left at the end of the series, possibly leaving it open to further stories. Maybe some shorts?