Hel is the daughter of Loki and a giantess and like her older brothers, she is not entirely human. Hel is born with decaying corpse legs which disgusts both of her parents. At age 14 Hel and her brothers are taken by the Gods to Asgard where she meets Baldr long enough to fall in love with him before she is thrown into the underworld to be its queen. Hel then spends eternity brooding about her lost love and getting revenge on the other immortals who have left her underground without another thought.
The review I read of this book described it as a good next step for Percy Jackson fans. I haven't read any Percy Jackson books for years but this is nothing like I remember of them. Hel's griping is somewhat funny at first as it seems so modern even as she is telling you about events from the Norse myths thousands of years ago, but I was so over it by about chapter three. There really is no story here other than hearing a disgruntled narrator tell her version of her myth. If you are not familiar with the myth, perhaps that is enough, but I'm no Norse scholar and I didn't find it compelling. What's more, I felt like quite a few things were repeated. A point would've just been made and then in the next chapter it was summarized again. It reminds me of those reality shows where you come back from the commercial and the narrator catches you up on what you just saw three minutes ago. I suppose there's not a lot to work with here since Hel is stuck in her own underworld and refuses to interact with any of the dead she oversees, but that's something the author should've considered when deciding to tell her story.