Dark Harmony

Pretty solid third book in the series. There was a lot of action, too much sex, and interesting world building. My main issue is that Callie hasn't really grown as a character even though her life has done a complete 180 and she still has petty thoughts and weird self-doubt. I think Thalassa was trying to write in a sort of PTSD sub-plot from the events of book 2 but it just came up as Callie being a whiny baby one moment and then a Strong Female Character the next and the two just don't mash up realistically. There's still a strong Twilight-vibe in that you have no idea why Desmond would be interested in this woman, even if she is half-siren, because of the maturity and just years lived difference - which is probably why the author threw in the “soul mate” trope in the last book.
A fun romp in a unique world, but not one you can think too much about before ruining your enjoyment.