This was really meh until the end when it switched to terrible. I did not care for either character and I didn't find their romance believable at all. The world-building/plot didn't make a whole lot of sense to me especially how Cale became the Queen's Assassin (aka the title). It's a spoiler so it won't be discussed here, but I felt like it could've easily been resolved.
The magic system wasn't well explained at all and was very convenient. There did not seem to be any particular limits, and whenever something needed to be done it could just be magicked away.
The "twist" ending really tipped it over the edge for me, as it's a "twist" I can't talk about it without spoilers.
Just overall this book was not great, would not recommend it.