Ariel and Flounder are swimming when their day is disrupted by a sea battle between a pirate ship and a navy ship. In the battle, one of the pirate’s boots falls overboard and sinks down to Ariel and Flounder. Ariel and Flounder wonder what the “thingamajigger” is, and whether it was what caused the commotion. Their fish friends try to figure out what the thingamajigger is, but all their attempts go badly.King Triton arrives and argues that humans are evil and only put bad things in the water, like hooks, nets, and pollution, so whatever the thingamajigger is, it must be dangerous. Ariel argues that learning about it might be useful, but Triton orders that Sebastian bury the thingamajigger somewhere where it can’t do any harm. Though disappointed, Ariel offers to help.
A group of gossiping clams hear that Triton is afraid of the thingamajigger, and start passing on the word that the thing is a menace to all those under the sea. The word eventually reaches Lobster Mobster and Da Shrimp, who decide to get the thingamajigger and use it to seize power.
Ariel and Sebastian bury the thingamajigger, but after they leave, a sea snail digs it up and climbs inside. When they see the boot apparently hopping all by itself, the clams spread the word that the thingamajigger is loose. Word of the emergency reaches King Triton just as Ariel and Sebastian arrive to declare “mission accomplished.”
Lobster Mobster takes the thingamajigger and tries to figure out how it works. He points it at a cliff and tells it to shoot. At that exact moment, a cannonball fired by the pirate ship happens to strike the cliff, causing an explosion. Lobster Mobster and the clams are all convinced that the thingamajigger must be a very powerful weapon.
Meanwhile, Ariel, Flounder, and Sebastian follow the boot tracks, and come across the crater left behind by the cannonballs. The clams inform the group that the thingamajigger caused this destruction, and that Lobster Mobster has it. Ariel decides that their only hope is to go to the surface to find out how the thingamajigger works and how to stop it.
Word of the thingamajigger’s destructive power reaches the ears of the Evil Manta. Sebastian catches up with Lobster Mobster and hides inside the boot.
Ariel and Flounder investigate the docks, and are terrified when they see humans unloading nets full of fish. Prince Eric arrives with his dog Max, and Ariel realizes that humans wear thingamajiggers on their feet. A porpoise is caught in a net and thrashes desperately. The ship captain yells for someone to get rid of it, and Eric volunteers. Ariel and Flounder are horrified when they see Eric pull out a knife, but to their surprise, instead of hurting the porpoise, he cuts it free of the net.
- Ariel: How can that be? A human who’s not evil?Flounder: Maybe we came to the wrong place.Ariel: I wish I could have seen his face.
Meanwhile, Sebastian tricks Lobster Mobster into thinking that the thingamajigger is alive and can talk. Lobster Mobster and Da Shrimp flee in terror, but before Sebastian can celebrate, the Evil Manta finds the thingamajigger. The Evil Manta is also fooled into thinking the thingamajigger is alive, and tries to form an alliance with it to rule the ocean together.
The Evil Manta arrives in Atlantica and threatens Triton with the thingamajigger. Though Triton does not give in, the fish and octopuses are so terrified of the thingamajigger that they immediately offer to surrender. But before the Manta can take the trident, Ariel arrives with two thingamajiggers! Having lost the under the sea arms race, the Manta is forced to flee.
Ariel explains that thingamajiggers aren’t weapons. Triton is upset that she went to the surface to find this out, but Ariel argues that learning more about humans was necessary to solve this problem. Triton orders her to dispose of the thingamajiggers, and Ariel does…by hiding them away in her new collection of human artifacts.
Tropes
- Correlation/Causation Gag: Lobster Mobster aims the boot at a cliffside to see if it's a weapon. The cliff just happens to be hit by cannonballs from the naval battle in the surface, convincing Lobster Mobster that it is a powerful weapon.
- Character Development: Ariel and Triton have both learned some lessons after what happened in "Charmed". While human items are still a Berserk Button for Triton, he knows that destroying one in front of Ariel will upset her, so he simply tells her to bury it. Despite her disappointment, Ariel goes along with this without too much argument, having learned that some human items can be dangerous.
- Entertainingly Wrong: A series of coincidences lead everyone under the sea to think that a boot is a terribly destructive weapon.
- Fishing for Sole: After Eric loses one of his boots, a sea captain suggests that he throw the other one into the sea, saying that he finds it funny when fishermen catch a boot by mistake.
- Gossip Evolution: The clams overhear Triton's concern about the "thingamajigger" and pass it along as him being afraid of it. By the time it reaches Lobster Mobster's ears, the clams claim the thingamajigger is some sort of powerful weapon.
- Guns Akimbo: Ariel does this with boots.
- Motive Rant: When Sebastian (pretending to be the thingamajigger) asks the Evil Manta what he wants to succeed at, the Manta has this to say:Evil Manta: Succeed at having my way, and not letting others have their way. Succeed at making everyone else’s lives miserable and hopeless. I want to stop all music, to abolish art, to destroy dancing! Besides, what’s it to you, thingamajigger?Sebastian: Er…just making conversation, Mr. Manta.
- We Can Rule Together: The Evil Manta makes this offer when he thinks the thingamajigger is alive.
- Weapon for Intimidation: The only use the thingamajigger has as a weapon. Ariel finds out that the “thingamajigger” is actually human footwear, but since no one else under the sea knows that, she is able to use two boots to scare the Evil Manta away.
