A Grim and Sunken Vow (The Hollow Star Saga 3)

Arlo and her friends must decide how far they're willing to go to depose a cruel ruler in this third book in the Hollow Star Saga that's The Cruel Prince meets City of Bones.
The die is cast.
The era of Spring is over.
Riadne’s bloody coup on the Summer Solstice changed Arlo’s life forever. In one fell swoop and a fool’s bargain, she lost both her family and free will to the newly crowned High Queen. Now, with Arlo forced to use her powers as Luck’s Hollow Star to help summon the rest of the seven deadly sins, Riadne stands closer than ever to achieving her dark goals.
And Arlo isn’t the only one trapped in a frightening new role. Her ex-Fury girlfriend, Nausicaä, is determined to do whatever it takes to stay by Arlo’s side, even if that means becoming Riadne’s pet assassin. Aurelian and Vehan, torn apart, struggle to survive on their own.
Meanwhile, Celadon has been revealed as Riadne’s illegitimate son—and heir to both Spring and Summer, the ultimate offense in the faerie world. But the High Prince has secret plans of his own, plans made all the more complicated when the beautiful and deadly immortal Hunter Lethe takes an interest in him…
Five budding legacies will need more than luck if they hope to stand a chance against the greatest adversary the Courts have faced. For nothing’s more dangerous than a faerie tale… except the one who tells it, and maybe what they’re going to need is no longer that story’s hero but its villain .