I would say this is very loosely based off the story of Rapunzel. Instead of a fragile princess locked away in a tower and sporting an extremely long hairdo, Selestra is tough, taught by a soldier in the Last Army (though she doesn't get to try that out till after she leaves the castle) with green hair that though is long, isn't long enough to climb down (no matter what Nox says). She is also a witch and heir to the only magic left in the Six Isles. This was a fun book to read and I do like that Selestra is capable, though when she and Nox work together, they are unstoppable. And that is definitely what is needed to end the reign of the immortal king Seryth (a completely awful guy who sucks the souls out of his victims to keep that immortality) and his all powerful witch by his side (Selestra's mother). There are lots of fun side characters like Micah, and Selestra's dressmaking friend, Irenya and sometimes I liked them better than Nox and Selestra. I liked also that it started with the festival but sadly it pretty quickly veered away from that.
This is a good standalone book and I enjoyed reading it. Still not a fan of that cover though.