Filet of Soul is the first part of the 8th episode of season 2, which first aired on September 3, 1997. In this episode, Dexter and Dee Dee give their pet fish, named Fishy, too many commands. As a result, Fishy suffers from exhaustion and dies. The siblings are then ordered to flush Fishy down the toilet, but after refusal, Fishy comes back as a ghost and haunts them.
The show begins with Dexter and Dee Dee making their pet goldfish Fishy do so many tricks and ends up suffering from overexertion. When Mom tells them that it is time for bed, Dexter thinks that fishy is playing dead and wants it to roll over, but he realizes that the fish is dead. The whole family takes Fishy to the bathroom for a funeral. Dad tells Dexter and Dee Dee that they must send Fishy to The Sewer Beyond where all significant pets go when they die and in the Sewer Beyond it can do what it wants. Dad tells the kids that it is time to say goodbye to Fishy while crying and walking away. Mom tells Dexter and Dee Dee that could get a new fish while telling them to flush the fish. While looking inside the toilet Dexter is about to flush Fishy, but Dee Dee stops him and puts the fish on the toilet lid where Dexter won't get to it. Dee Dee tells Dexter that they will find a decent burial in the garden tomorrow while sending Dexter and herself to bed. But when they gone Fishy's spirit leaves his body and begins to haunt the house. While Dexter is about to go to sleep, he says goodnight to his picture of Albert Einstein, his Major Glory Action figure, and the ghost of the dead fishy, but when he realizes that he is seeing a ghost, Dexter and Dee Dee begin to run into each other's room screaming several times and then crashing into each other. Dexter questions Dee Dee about seeing the fish ghost, but she denies it and says she like to run around and scream real loud. Dee Dee begins to mock Dexter about being a fraidy cat but when she sees the Ghost of Fishy, it kisses her. Dee Dee and Dexter knows that it is time to suit up and begins to get ready. Dexter gets out his ghost busting gear and begins to look for the ghost and almost captured it. While Dexter is still walking down the hallway, Dee Dee, who is in a white sheet, alarmed him and almost shoot her. Dexter demands to Dee Dee why is she in the white sheet and Dee Dee says that she wants to scare the fish's ghost. Dexter begins to cry saying that they will never catch the ghost fish, but has an idea. Using a bag of gummy worms and a fishing pole, Dexter and Dee Dee begins to lure the Fishy's ghost using the fishing pole and a gummy worm as bait right into a pile of gummy worms. While the spirit is busy eating the gummy worms, Dee Dee captures it and Dexter uses his ghost busting gear to capture it immediately. Thinking that their work is done, Dexter goes straight to bed while Dee Dee goes to the bathroom to brush her teeth after eating some of the gummy worms on the floor. As Dee Dee is brushing her teeth, a bunch of spirits of deceased pets from the Sewer Beyond capture her, and Dee Dee manages to wake her brother up and tell him to go to the bathroom. Dexter sees Dee Dee getting flushed into the toilet and tells Dee Dee to come out of it, but Dee Dee tells him that she is trapped in the Sewer Beyond and the pets captured her and won't release her until Fishy is given the burial. Dexter tries to reach for Fishy, but his arms are too short, so he uses a plunger to get Dee Dee out and order her to flush the dead fish's body which she does. But when they flush the fish, the angry pets summoned a giant octopus tentacle to grab Dee Dee and pull her back into the Sewer Beyond. As Dexter begins to struggle with the tentacle, he says they flushed the fish, but Dee Dee tells him that Fishy's spirit is still in the trap. Dexter hits the hook on the trap, managing to open it, then Fishy's spirit flies to the toilet and it all ends. Fishy then enters the Sewer Beyond with a smile on his face. Dad warns them, again, that early morning is his special bathroom time and the next scene reveals that Dad gains golden glowing eyes with slit pupils and sharp teeth and he laughs maniacally.
When Dexter said "Who you gonna call?!" and wearing the ghost-capturing device they were references the Ghostbusters film franchise.
The entire episode is a reference to a 1982 supernatural horror film by Tobe Hooper, Poltergeist.
The episode name is a pun on a sole, a type of fish, and "filet of sole", a type of food.