The people of Oak Grove have stopped up the creek that used to run through their town, because they don't like to be anywhere near water. Eli and Trevor McGill, called Eel and Trout for their fish-like quickness, don't fit in at all with their strange fondness for meals of raw tuna and seawater. Their best friend, Martha Glimmer, feels out of place too, heartbroken after her mother's death. Dreaming of escape, the three run away, but a flash flood forces them home again, to think about what would make them truly free and face the truth - that Trout and Eel are the sons of a mermaid.