After kissing King Triton goodbye, Ariel is doing her usual thing of hunting down human things, just as Sebastian is doing his usual thing of trying to discourage her and Flounder is doing his usual thing of being supportive but nervous. The human things accidentally fall from the ship (owned by Prince Eric, Grimsby, Max, Chef Louis). But today is special, Ariel tells them, because Gabriella and Ollie (whom they first met in "Wish Upon a Starfish") are coming to visit.
When Gabriella and Ollie do arrive, the whole gang hang out in Ariel's grotto reminiscing over their previous adventures together, surrounded by Ariel's collection. But unknown to them, they're being spied upon by Flotsam and Jetsam, Ursula's lackeys.
As she watches them, Ursula hatches a plan to take advantage of the Atlanticans' fear of humans. Using one her potions, she casts a spell on Ariel's eggbeater, causing it go haywire and attack Atlantica. Ursula then announces her arrival to the panicking Atlanticans, offering to stop the crazy eggbeater in return for being given the crown. Fortunately, Ariel and Gabriella manage to stop the eggbeater on its path of destruction before the rest of the Atlanticans can respond to the offer. Ursula huffs off, temporarily sideswiped.
Ariel knows that something's up, and deduces that the sea witch has found the location of her secret grotto and her collection of human things. So she and the gang decide to move all her treasures to a new location where Ursula won't find them. They manage to get the items out of the grotto, but before they can move all of them to safety, Ursula sets off another spell — this time causing all of Ariel's human things to go berserk.
It's too much for the gang to stop on their own this time. When Ursula reappears to try and schmooze the Atlanticans into letting her become Queen, Ariel quietly sneaks off to Ursula's lair to find a magic potion to stop the possessed items.
By the time Ariel gets back to the scene of the crime, her treasures have formed a dangerous whirlpool. Ariel hesitates, knowing that if she casts the stopping potion towards them, her treasures will be destroyed also. But in the end, she does what needs to be done, leaving Ursula to skulk off and live to fight another day.
Her friends immediately try to comfort Ariel over the loss of her treasures. But although she's sad, she knows that her friends are more important than any mere objects. And besides, she can just start a new collection.