It should never take a book 81% of the way through the story for the main character to realize the main plot point, especially when the reader figures it out almost immediately.

Spoiler

The whole "I'm Persephone reincarnated" thing, which was poorly executed in every way possible, to add insult to injury.

Piper spends this entire book crying, whining, or both, and fails utterly to have an ounce of agency for a single sentence. Her mother controls her, her best friend talks her into getting a tattoo, Hades and Ares throw themselves at her like neither of them has gotten laid in centuries, and the whole plot centers around Piper figuring out who she is, which she doesn't because she's an idiot.

One of the worst Greek myth retellings I've ever encountered.