The writing is so simple, but what I appreciate about the story is that it's full of mystery and it doesn't feel the need to over explain things. You're never really sure what Jessie is or what her mother is or what really went on at The Sands all those years ago.
This book is actually surprisingly dark for a children's book, but I guess the best ones always are.
There are also so many layers and themes in this slim volume — loss, letting go, father/daughter relationships, girls growing up without their mothers, illegal/unethical activities, xenophobia, ignorance, and how easily people fear whatever they don't understand.
Along with The Changeling Sea and Seal Child, this one has that whole trope of mysterious sea creatures returning to the sea and leaving loved ones behind that I find really fascinating for some reason.