Rainbow Fish gets a bad report card (he gets a "C"). But when he accidentally spills ice cream (from a kelp gusher milkshake) on it at Wanda's, his parents mistake the "C" grade for an "A". Rainbow must prevent them from meeting Principal Gefilte and learning the truth. For getting a "C", changing his grades, and lying that he got an "A", he is cave grounded by his parents until he gets his grades up. This means until he gets his grades up, he is "cave grounded" except for school (meaning he can only leave the house to go to school while cave grounded).