Adeline, daughter of an earl, was offered an engagement from the Dragonkin Realm. They wanted her to be the "Mate" for the third prince.
All Dragonkins have to find their "Mate" and take them to their castle built on the floating island and live together, although their lifespans might be different.
Adeline was fragile...she could hear that everyone in the castle criticized her as someone not worth being the Mate to the prince. Even the prince himself seemed to hate her. She ended her miserable life by someone's poison.
250 years after, Adeline was born to the same world. And again, she received an invitation from the Dragonkin for a ball to find their Mate. She tries to run away...not knowing that there was a secret beyond this invitation.