Sink is a mermaid fantasy with a somewhat romantic subplot. I wouldn't call this a romance, because the relationship itself between the love interest (Eddie) and Pauline (the protagonist) was underdeveloped and largely unexplored. The two characters didn't get to spend any time together outside of chasing the main plot, meaning their chemistry was never established. Eddie—a fisherman who evidently cannot swim—was not particularly likeable character, either, expressing some chauvinistic traits, which didn't help me feel any better for Pauline's apparently intense attraction to him.
The main plot line sees Pauline seeking out a way to dethrone her evil mother, Queen Calypso. The story began with a distressing scene, establishing Pauline's motivation for change. When Eddie is thrown into the mix, things only become more tense and difficult. Unfortunately, as soon as the couple embark on their journey out of the kingdom, the story begins to deflate. Any tension developed is soon lost when obstacles are overcome with enormous ease. This trend continued into the climax, where I found myself thinking "That's all they had to do this whole time?"
Rhines's style was her saving grace. Her words flow smoothly, her style is engaging, and she has a talent for balancing introspection with vivid, grounding scenes. Her writing was easy to read, though lacked some attention to detail in areas (for example, the mermaid's legs or knees were referred to a few times, and some of the underwater physics didn't make much sense).
This book may appeal to readers who just want an innocent, easy fantasy read with simple world building and a taste of surface-level romance.