With Roman gone, Haven seeks her revenge on Ever and Jude. Haven targets Ever by trying to turn her against Damen. This doesn't work until Ever finds secrets of Damen's past, causing her to grow closer to Jude. Haven, addicted to the elixir, is desperate for any she can get, while Ever is desperate to get the antidote. They come to a compromise, but when Haven goes back on her word, things become deadly.
What I love about series is that while each book has its own climax, the series itself also has a climax. I think that Night Star is the climax of the Immortals series. There was tons of action, and kept me wanting more after each page.