Celeste is a shy princess who loves mathematics. She was abused at a young age when forced into a marriage way too young. She suffered from mental and physical abuse. In Assassin's Gambit she was saved by her sister-in-law. Now many years later under the more caring upbringing of her brother she is happy.
Rayn is a foreign prince who has many misgivings towards the Kjallans. Celeste's father had been a horrible monarch so Rayn struggled to trust them. Rayn and Celeste end up taking a ship to visit one of Kjall's provinces and end up in an assassination attempt. As the two go through this adventure of determining who the assassins were, Rayn is able to get to know Celeste a little better.
The biggest problem I had with this book was that parts didn't flow well for me. Rayn seemed to be fine with everything at one moment and then out of nowhere he freaked out at Celeste because of her family and country. I really was baffled as to what set him off. It just didn't seem like a natural way to act.
I loved the scenery a lot with this book. At one point they even get to experience Inya which has volcanoes that the Fire Mages have to control to protect the people. I loved learning about this new mage type. So far with every book in this series, Raby introduces us to another mage type. I really like her magic system.
Honestly, if arranged marriages turned into love matches is your thing, you would probably really enjoy this book. It just wasn't for me. I am excited though for the series to continue.