For actions made in the first book, Skin of the Sea, Simi now has to serve a new God, who is untrustworthy. She learns that she has to fight to protect herself and others. She is on a quest to capture the soul song that would save her and the people at the bottom of the ocean but there are demons who want to harm her and collect more bodies in her path.
The romance between Simi and Kola continues in this conclusion and Simi forms new alliances.
However, this book reads more violent than the first one. They are at war with a God who wants more casualties. The fight scenes are well written and explicit but not too gory.
The ending is satisfying but I did not enjoy Soul of the Deep as much as I did Skin of the Sea. There were too many characters with similar names, also the names were similar to places mentioned. That got annoying and confusing. I switched back and forth between the physical and audio book to hear the pronunciations but the narrator did not clarify all that much.