I would give it a 2.6/5 (received as an ARC)
Starting out, I enjoyed the book. I thought the plot was interesting, and the characters easy to follow. Pretty early on, I did notice some typos that were hard to ignore and were more or less constant during the entire read (I was an ARC reader so I hope this was fixed before being published). The friend was found pretty fast, and I was curious to see where it would lead, and sure enough the investigation continued. But from that point it started falling a little flat and the further I read the less I wanted to finish the book.
The entire middle of the book I felt like the plot was lost and instead had a lot of info about the relationship between Persephone and Hades that I wished took more of a back seat to the plot. I kept waiting for something to happen or for the FMC to get taken, but it never did. When she was injured, it was only until the start of the next chapter then she was totally fine, and the time between was hard to follow. At one point I think we found out it had been 9 or so months from when they met each other, and it was confusing since it didn't seem like much time had passed.
I think the book could've been shorter since not a lot happened in the first book. There was a little bit of world building (earth, the underworld and a liiiittle of olympus), not a ton of character development, the friendships I think were understated and I would've like to see that trio a lot more and in general more of the mystery around what was happening. It felt like they had all the info they needed and nothing ever happened.
I understand that to have a story with high powered individuals, you don't want it to have a fast finish, but I find it hard to believe that Hades would've let one character live after what she did, and that they didn't end another character once they found who it was. I think there should've been more explanation on that part since it really was hard to believe.
I do think it will be interesting to see where this story goes and how it develops, and since there was a bit of building in book 1, I do believe that book 2 will be more plot driven in a way that I am excited to see.