Help! I’m a Fish

With their parents out for the night, Fly and Stella slip away from Aunt Anna's watch and head to the shore to fish. A rising tide drags them toward the boathouse of Professor MacKrill, where his strange world begins to reveal itself. Their curiosity sets the stage for the extraordinary events to come.

MacKrill explains his experiments: a potion that turns humans into marine animals and an antidote that can restore them. He speaks about climate-change-driven transgressions and a sea-facing future he hopes to create. The children realize they are in the middle of a dangerous, world-altering scheme.

Stella mistakes the potion for lemonade and drinks it, turning into a starfish. Fly panics as he watches the change and accidentally tosses the bottle out a window into the sea. The escape plan becomes urgent as Stella's fate becomes uncertain.

Chuck discovers Stella's transformation after reviewing footage of the moment. Realizing time is running out, the trio resolves to search the ocean and bring Stella back to land. They set out on a rescue mission that will push their fears to the limit.

The trio's search is interrupted by a violent storm that swamps their improvised craft. The boat sinks, separating the kids and starting an arduous fight to survive at sea. With Stella still changed, they cling to hope that they can still rescue her.

Amid the chaos, Fly drinks the potion and becomes a California flying fish, while Chuck becomes a moon jellyfish. Stella remains a starfish, completing their odd transformations. The trio must adapt to their new bodies and press on with the mission.

Bill and Lisa return home with Aunt Anna to find Stella missing and Fly's gear missing as well. They search the beach, eventually finding Fly's rollerblades as the only clue to his whereabouts. The adults fear the worst but refuse to give up.

MacKrill arrives to reassure the adults and shows them a video confirming Stella's transformation. He stresses the urgent need for an antidote and invites the adults to help rescue the children. The family agrees to pursue every possibility to restore them.

Underwater, the leaking antidote attracts a lemon shark and a pilot fish, granting them intelligence and humanoid traits. The pilot fish proclaims himself Joe and uses the antidote to form an underwater civilization that seeks to revolt against humanity. The shark becomes his loyal, dim-witted adviser.

Fly, Stella, and Chuck travel to Joe's domain, a sunken oil tanker, hoping to steal the antidote. They are captured and interrogated by Joe and then imprisoned by a militaristic king crab.

Sasha the seahorse frees the children from captivity, and they realize their only hope is to replicate the antidote by gathering ingredients from around the ocean. They prepare to pursue a risky plan that could restore their humanity.

Joe's army closes in as the team completes the antidote. Joe drinks the last of the original antidote, mutating from fins to hands, and prepares to strike. Fly lures him into drinking repeatedly by challenging his intellect, causing him to mutate again and drown.

Fly drags the antidote back into MacKrill's lab and Chuck uncorks it as Lisa and Anna reopen the flooded lab. Stella and Chuck become human again, reuniting with their parents and MacKrill. A stuffed fish is mistaken for Fly's body before the real Fly arrives with a broken leg, and Sasha is transformed into a real horse that Stella joyfully rides along the shore.