Peter is running through a misty forest, fighting an ant monster. He tries zapping it, but it's immune, then it cuts the cord to the proton pack. The ant monster chases Peter up a tree, but then it turns out to all be a dream he was having while napping at his desk. Ray then gets a new ant farm in the mail, but Peter angrily declares that he hates bugs and the world would be better without them.
Winston and Janine, meanwhile, are at the museum, looking at an exhibit that resembles the monster from Peter's dream. Janine reveals to a bored Winston that it's an Egyptian insect god called Aphsai, and then they attend a lecture on Aphsai. The lecturer reveals that Aphsai and his followers were kicked out of Egypt never to be seen again, and took the alleged source of his powers, the Crystal Capstone, with them. He opens a golden scarab from the era, which then causes an earthquake, and causes the Crystal Capstone to start glowing underground. Then, a mandible emerges from it.
After the earthquake, a whole lot of bugs start swarming both inside and outside the firehouse, confusing Egon since bugs usually swarm before earthquakes. Then, in Central Park, giant bugs start crawling out of the earth. Ray and Egon fly off in Ecto-2, while Peter and Slimer drive off in Ecto-1. Egon and Ray get attacked by a giant dragonfly and crash-land in a pond in Central Park. They regroup with Peter, Slimer, Winston, and Janine at Ecto-1, and the Ghostbusters change into their uniforms.
They then observe that the bugs are building something, and that they appear to be supernatural in nature. Peter goes to get the ghost traps to trap them, but finds beetles stripping Ecto-1 and is then tied up with webs and carried away and underground by giant spiders. Slimer follows after, while Egon concludes that the bugs used to be normal bugs and that zapping them returns them to normal.
The spiders bring Peter to the Crystal Capstone, where Aphsai says he plans to sacrifice Peter. The others pump honey out with a fire pump to distract some ants, while Aphsai reveals that he wants to lead a bug apocalypse. Janine then realises that the thing the bugs are building is a recreation of Aphsai's temple.
The other guys search for Peter, and find Slimer, who shows them Aphsai. He reveals that he plans to put the capstone on the temple once it's built, and then gain infinite power using the capstone and the sun. Everyone fights Aphsai, eventually destroying the capstone, making him turn into sand and the bugs return to normal. Peter uses this adventure as further proof bugs are nothing but trouble, but Egon counters they're important.
This episode provides examples of
- Artistic License – Biology: Egon calls some spiders "insects". Insects are defined as bugs with six legs; bugs with eight legs (such as spiders) are called arachnids.
- Attack of the 50-Foot Whatever: Apshai makes some bugs grow giant.
- Badass in Distress: Peter gets kidnapped by the spiders and taken prisoner by Aphsai.
- Bait-and-Switch: The first scene turns out to be a dream.
- Bee Afraid: Invoked when Aphsai hexes bees to want to sting all humans to death.
- Big Creepy-Crawlies: Invoked when Aphsai deliberately possesses some bugs and makes them grow huge.
- Big "NO!": Aphsai yells, "NO!" as he's being trapped.
- Bullying a Dragon: Peter calls Aphsai ugly, causing him to grab him.
- Delicious Distraction: Invoked when the non-Peter Ghostbusters distract giant ants with honey.
- Demonic Possession: Aphsai makes the giant bugs by possessing normal bugs.
- Distressed Dude: Peter gets captured and almost sacrificed.
- Don't Go in the Woods: Peter's dream takes place in a dark, spooky, foggy forest with an ant monster.
- The End of the World as We Know It: Discussed — to achieve world domination, Aphsai wants to have all of humanity killed.
- Evil Gloating: Aphsai gloats about his evil plans to Peter.
- Evil Sounds Deep: Aphsai has a deep voice.
- Friend to Bugs:
- Ray buys an ant farm, and he's the one to spring to the defense of the fleeing bugs.
- Discussed when the others consider Peter possibly making friends with the butterfly who lands on him.
- Giant Spider: Some of the giant bugs are spiders.
- Glowing Eyes of Doom: Several of the bugs, Aphsai, and the dream monster all have glowing eyes.
- Gross Gum Gag: When Peter is under his desk because of the earthquake, he picks up some gum, cringes, and asks who left it there.
- Layman's Terms: When the dragonfly first shows up, Egon calls it by its Latin name. Ray is confused, so Egon has to explain.
- Nightmare Sequence: At the beginning, a napping Peter has a nightmare about an ant monster.
- Parrot Expo What: When Egon calls the dragonfly an "anisoptera", Ray says, "Anisopter-what?!".
- Pre-Asskicking One-Liner: Janine says, "Bug off!" before shooting one of the bugs.
- Psychic Dreams for Everyone: Peter dreams of fighting a giant bug, then everyone has to actually fight giant bugs.
- Pun:
- Peter mentions the bugs are "turning the Big Apple into the Big Applesauce".
- While fighting one of the bugs, Janine tells it to "bug off".
- Punctuated! For! Emphasis!: As Peter wakes up from his dream, he yells, "I! Hate! Bugs!".
- Red Eyes, Take Warning: Aphsai has red eyes.
- Red Is Violent: The ant monster in Peter's dream is red and attacks him.
- Say My Name: Slimer yells, "PETER!" as he's being kidnapped.
- Scary Stinging Swarm: Subverted — a swarm of bees flies out of the drawers, and everyone except Ray freaks out, but then they realise they're fleeing rather than attacking.
- Screw This, I'm Outta Here: Defied — Peter, upon meeting Aphsai, tries to run away, but is stopped.
- Shout-Out: The title parodies 20,000 Leagues Under the Sea.
- Sizeshifter: Aphsai can grow as an attack.
- Skewed Priorities: Egon is more concerned about his jars of fungi breaking than about getting to safety during the earthquake.
- Take Over the World: The reason Aphsai wants to destroy humanity is because he wants bugs to rule the world instead of humans.
- Talking in Your Sleep: Peter talks in his sleep just before waking up from his nightmare.
- Theme Music Power-Up: The theme tune plays as Aphsai is being fought.
- Why Did It Have to Be Snakes?: Downplayed — Peter's hatred of bugs is mainly because he finds them gross and ugly rather than because of any fear. That said, he is scared of the first swarm.
