Girl at the bottom of the sea

"Sophie Swankowski is the hero from the stories she's been hearing all her life: she's the girl who will save the world. Or so she's been told. Now she and her unlikely guardian, the gruff, filthy mermaid Syrena, must travel the pitch-black seas from broken-down Chelsea, Massachusetts, to Syrena's homeland in Poland. Along the way, Syrena will reveal the terrible truth about her past, and teach Sophie about the ages-old source of her newly-discovered power. But left behind in Chelsea, without Sophie to protect them from the dark magic she's awakened, what will become of Sophie's friends and family?"--Page 4 of cover.