Ned Finn is a boy who knows what he wants. He wants an entertainment system for his room. He wants a break from his boy-crazy sister, Stacey, and for his little brother Billy to leave him alone. Heck, he just wants a normal set of parents.
But when Billy eats some of their father's experimental fish food and turns into a cod, Ned just wants to turn him back. Not only are Bill's new gills drawing the attention of the local school bully, they also attract the interest of Madge Sprod, an international spy with an evil plan.
When a slippery showdown at the local aquarium pits Ned and Billy against both their enemies "and" a killer whale, will Ned be able to save the day before his little brother becomes fish food?