First, let me get this announcement out of the way: Radiant Shadows is not about Aislinn and Seth, or even Aislinn at all. Of course that's disappointing to those of us who want to know what happens next to our couple now that Seth is faery, but that story must wait until another story is told. Then I suspect we will know how it all comes together, but if you go into Radiant Shadows expecting not Aislinn and Seth, but instead a story that stands on its own merits, you will come away from the reading with a much more satisfied frame of mind.
That said, Radiant Shadows focuses instead on the halfling Ani and her importance to the land of Faerie and Devlin, the brother of Sorcha, Queen of Faerie. Devlin has always done his sister's bidding (and tried to get along with her evil twin Bananach as well) except in one slightly major thing: he did not kill Ani when she was a child as Sorcha instructed him to do. Oh, and one more thing: he allowed a mortal, Rae, to inhabit Faerie without his sister's knowledge or permission. Devlin's lapses have stayed hidden relatively well until Ani starts to come into her own powers, and Rae, who is now a dreamwalker, unwittingly supplies Sorcha with the power to watch her newly reborn son Seth in his mortal life. To say things deterioriate at this point is an understatement: Ani suddenly finds herself hunted, Devlin must determine where his loyalties actually lie, and the courts are all in disarray. The one mention we get of Keenan is that he's missing, which cannot bode well for Aislinn or Seth, or even Irial and Niall.
Radiant Shadows began as pure confusion for me; it had been a year since I'd read Fragile Eternity and the intricacies of the courts and the Hounds was lost on me totally. The absence of Aislinn and all that I'd come to know of Faerie at first left me cold, but once I started to sort out the situation, I found that Radiant Shadows itself was a well written labyrinth with twists that I could not predict. I can see now where Ms. Marr was leading us and that this story needed to be told in order to get all of the details set up for the final book, but I would very much have appreciated some sort of reminder of who the Hounds and the Hunt were and perhaps a diagram showing where all the courts reside. (This being an ARC I read, it is possible the final copy will indeed include these things). This book is gorier than the others in the series, and the darkness that permeates the world Ms. Marr created is definitely growing. Now that I'm done, I can appreciate the world of Faerie and its intricacies; I just feel the need to warn those who are hoping for a smooth continuation into the lives of Aislinn, et.al that that's not what this book is about. Still, it's definitely well written and gripping, and I can recommend it not just as a filler story, but one that stands strongly on its own if given the chance.