When Spencer shoots a Jaws-style movie in his pool, Billy's ectoplasm turns the film's harmless goldfish star into a fearsome aquatic monster.
Spencer is trying to film a movie in the Cobra mansion’s swimming pool, but exclaims angrily when Billy gets in the way of his shot. Billy apologizes but argues that he’s sweating and Spencer is hogging the only shade, and Spencer asks since when ghosts sweat. Billy suggests going inside, but Spencer says he promised his MeTube fans that his next movie “Fatal Fins” would be online tonight. Spencer asks Billy to hand him the film’s star, which turns out to be a small goldfish. Billy questions how it could be scary, and Spencer explains that it will happen through special effects. Hugh then walks onto the deck and finds Spencer “talking to a fish” and assumes it’s a negative effect of the heat, suggesting a swim in the pool to cure it. Spencer stops him and explains that he’s filming. Hugh expresses his support but asks Spencer to hurry up and goes back inside.
Spencer tries to resume filming, putting the goldfish in the water, but is interrupted once again by Billy jumping into the water and splashing him. Billy swims around, trailing ectoplasm into the water. The goldfish absorbs the ectoplasm and transforms into a monstrous mutant with sharp teeth. Billy dives underwater and the fish attacks him. He bursts out of the water with the fish biting onto him, which Spencer films. Billy angrily says that the fish is trying to eat him, which Spencer says can’t happen, and Billy removes the fish and places it back in the water. Spencer is satisfied with what he filmed, Billy asks what kind of goldfish it was, and Spencer explains that the ectoplasm from Billy’s sweat must have transformed it.
Spencer gets some more footage before Hugh calls from inside asking if he’s done yet. Spencer calls back that he’s almost finished and tells Billy they need to remove the fish from the pool. Spencer tries to use a net, but the fish shreds it. When Hugh comes outside and is about to swim, Spencer tells Billy to do something, and Billy places a piece of a nearby cactus plant into Hugh’s trunks, causing Hugh to scream and run inside. Spencer follows Hugh and tells Billy to get the fish out of the pool. Back inside, Spencer removes the cactus spikes from Hugh and turns up the AC, suggesting they stay indoors. Billy baits the fish into jumping back into the fishbowl, but it breaks through the glass and escapes back into the pool. As Billy informs Spencer of what happened, Spencer hears his mom saying she was ready to swim. He goes back inside to find his whole family in water polo gear, ready to go. Spencer tries to stop them and suggests that since it’s so hot out, they do something inside instead, turning up the AC again. The AC then breaks and Hugh attempts to fix it, only breaking it further. The Wrights try to go back outside but Spencer stops them once again by reminding them to put on sunscreen.
Billy once again tries to bait the fish, but it slaps him away with its tail. Spencer finds out that the fish still hasn’t been caught and panics once again as his family members are about to get into the pool. He tells Billy to suck up all the water and Billy does so, but the fish goes down the pool drain. The Wrights run outside to find no water in the pool and when they ask what happened, Spencer says it must have evaporated. He gets the hose and starts filling the pool and suggests that his family go cool down in Hugh’s meat locker. They go back inside, exasperated, and Billy spits all the water back into the pool.
Spencer hears a scream from inside and goes to investigate, telling Billy once again that they need to catch the fish. Billy goes for the drain and Spencer finds Jane fighting the fish from the kitchen sink. He hits it away and the fish goes back down the drain. Billy pops up and says he tried, suggesting going to the WiFri, which Spencer angrily says that they can’t do until they catch the fish. They then hear another scream from the bathroom and find Jessica trying to fight the fish in the bathtub. It smacks her into the wall and Spencer tries to wrestle it, reminding Billy that he’s supposed to be helping. Billy tries to catch the fish with his finger, but it pulls him back through the drain.
Hugh then calls from the pool deck that there was a fish in it and Spencer gets a fishing pole, but Hugh takes it from him and suggests he try to catch it. He suggests Spencer film him doing so and Spencer starts recording as Hugh explains his method. The fish, still dragging Billy through the pool, bites onto the bait and nearly drags Hugh into the pool. Spencer holds onto him and the fish continues to chase Billy, wrapping the fishing line around the pool’s pipes. Billy cuts off the fishing line and helps pull Hugh out of the water. The fish is dragged out too and Spencer throws his camera at it to stop it from attacking. Hugh and the fish, with Spencer’s camera in its mouth, both fall onto the deck. Spencer pulls the camera out of the fish’s mouth to find it ruined. Hugh expresses that he’s sorry about Spencer’s camera, but Spencer says that some things are more important than movies. The ectoplasm drains out of the fish, turning it back to normal, and Billy re-absorbs the ectoplasm. Hugh grabs onto the fish and as Jane and Jessica come outside. Hugh suggests that the heat made him think the fish was much bigger and insists on everyone getting into the pool. Spencer and Billy put the fish into a cup of water.
Spencer shows Billy the footage he captured of the fish terrorizing his family which he compiled into the trailer for “Fatal Fins: Part 1.” When Billy questions that “part 1” Spencer insists that they just have to make a sequel. He then spots a fly and starts planning out loud for another film, this one called “Fatal Wings.” Billy gets excited and gathers up some ectoplasm, throwing it towards the fly as the episode ends.