“And they all lived happily to the end of their days...”
Finally, we come to the end (Other than Stars Above). You can read the rest of the series here: Cinder, Scarlet, Cress, and Fairest.
Winter is Levana's stepdaughter, cousin to Cinder/Princess Selene. Many Lunars believe that she is the legitimate heir to the throne, and the people love her, so Levana hates her. Winter doesn't use her Lunar gift so she is slowly going mad. In order to get her to break, Levana manipulated her into cutting her face. Winter didn't break, and she still has the scars on her face.
Winter is in love with her childhood friend Jacin Clay. He joined Team Cinder last book, betrayed them at the end, but is kinda on their side anyways. His true allegiance lies with Winter. Winter asks for Scarlet as a pet, and gets to keep the poor girl. They form a strange friendship.
Meanwhile, Team Cinder decides to return Kai. Their new plan is to change the wedding venue to Luna. They will then sneak onto the planet and rally the poor, working class Lunars into fighting Levana. What they don't count on is an outbreak of Letumosis, which we just found out in Cress can infect Lunars now.
So the whole gang is on Luna, reuniting as the story goes. There's some angsty stuff about how far you can go before becoming like your enemy, how much you should sacrifice for the greater good, all that good stuff. We do have a lot of characters at the end, and a lot of plotlines to cover, but I think they are handled well. It was a satisfying conclusion for me, and I'll miss the characters I've come to know.