A Kingdom of Flesh and Fire is book 2 in the series. Book 1 is called From Blood and Ash, book 3 is called The Crown of Gilded Bones, and book 4 is called The War of Two Queens. The author mentioned there will be 6 parts to this series. She also anticipates writing a spin-off series as well.
Nykthos is the King of the Gods. In A Kingdom of Flesh and Fire, we only learn a small part of what there is to know about this God. He has an affiliation with the Wolven and therefore also with the night. He can turn the sky during the day into dark.
For people who aren’t familiar with From Blood and Ash, it will seem like there is a love triangle.In From Blood and Ash, Poppy’s love interest is Hawke. However, in A Kingdom of Flesh and Fire, it is Casteel. That said, both are one and the same person. So there is no love triangle, only some confusion with names and identities.