Moving home has not been much fun for Jimmy and his family, least of all for his fisherman father who had to leave the sea and his treasured boat behind. Then, out of the blue, Jimmy meets Major Gregory, an elderly gentleman and prize collector of koi carp.
Soon Jimmy is hooked and wants to learn everything there is to know about these gentle orange giants. But then he discovers something he'd rather not have known; thieves are planning to steal the Major's beloved army of giant goldfish, the whole pondful! Jimmy knows he's got to help, and before long he finds himself in deep, and very dangerous, water!