Help! I'm a Fish!
Fly is first seen making a fish hook and was about to go fishing when his parents Bill and Lisa told him that they are going out and his Aunt Anna is going to babysit them along with his cousin Chuck, much to his annoyance. When Aunt Anna fell asleep, Fly decided to get out and go fishing. He brought Stella, who was still awake, and threatened Chuck that he would break the backup of his work if he doesn't come along. After a while of fishing, they had to escape the tide, and then they met Professor MacKrill. Few moments later, Fly wondered where Stella was. The three searched for her, but all Fly could find while looking was a starfish. When he prepared to throw it in the ocean, Chuck had just found out that the starfish in fact WAS Stella who had drunk the fish potion the professor had made.
So Fly, Chuck and MacKrill hurried up and searched for her. But since the ocean was deep, making it impossible to see her, Fly decided that he would drink the potion too and keep looking underwater. Even though the professor said he would only have 48 hours to drink the antidote or he would be a fish forever. He still wanted to take that chance and find his sister, so he drank the potion, jumped out and turned into a California flying fish. When he found Stella, he cheered her up by telling her that they were now fish and how cool that was. They met Chuck, who had turned into a jellyfish when he drank the potion since he couldn't swim and was now looking for the antidote, which was lost when the storm got worse. They found out that the evil fish Joe had the antidote and that it wouldn't be easy to get it back from him.
After escaping Joe, Fly decides to make an antidote on their own, since all ingredients required are from the ocean. But as soon as they had gotten the last ingredient from a giant octopus, Joe arrived with his whole army, but was restrained by after promising Fly his position as commander. When the children tried to flee, Crab cornered Fly and they had a short standoff, where Crab wounded Fly badly and drank the antidote himself, causing him to grow and his claws to transform into hands. Now dying, Fly didn't think they could make another antidote in time, thus not be able to get back home at all. In the end, he was "using his brain...for once" and pursued Joe, who had stolen a spare bottle of the antidote in MacKrill's lab. When he caught up to him, he asked Joe questions that required him to drink more and more of the antidote, and in the end he became a grotesque human who couldn't breathe underwater anymore, thus drowning. Fly got the antidote back, but was thrown away before being able to take a sip.
Later, Fly emerged from a water pipe, human again, wounded but happy to see the others. The next day, his broken leg had been bandaged, and he was playing on Chuck's computer.