16-year-old Ruby Gillman is as clumsy as she is adorable. She desperately tries to find her place at Oceanside High School, where she feels like she’s completely transparent. She gives tuition in maths to a young skater she is secretly in love with, but who only seems to admire her ability to solve equations. And anyway, she can’t hang out with the most interesting students in high school, because her mother, who overprotects her, has strictly forbidden her to swim in the ocean. But the day she disobeys him and breaks this golden rule, she discovers that she is the direct descendant of the line of Kraken warrior queens, and that she is destined to ascend the throne hitherto occupied by her great -mother: the warrior queen of the Seven Seas. The Kraken are sworn to protect the world’s oceans from the greed and vanity of the mermaids, their sworn enemies. The only real problem for Ruby is that she’s going to have to go up against Chelsea, the prettiest and most popular new girl in high school who just happens to be a mermaid. Ruby will then have to embrace her destiny and impose herself to protect those she loves the most.