En route to Goldenrod City, Ash and his friends stop by a lake. Misty lets out all of her Pokémon so they can swim, but Psyduck has to be quickly rescued after it panics. Ash sends Totodile out too; he spots some Magikarp and uses his Water Gun to toss them into the air. As everyone is having lunch, Totodile sees an Azumarill sitting on the shore and singing. Totodile immediately falls in love with her and runs over to dance in front of the Azumarill. She isn't impressed, however, and blasts it with a Water Gun. Azumarill walks away, but Totodile follows her.
At the table, the group sees a Golduck in the bushes. Misty wants to catch it, but Brock urges her to wait since it seems to be looking for something. Shortly after, Golduck's Trainer Trixie arrives. Brock immediately tries flirting with Trixie, but Misty pulls him away. Ash apologizes for Brock's behavior and asks Trixie if she lost something. Trixie replies that she is looking for her Azumarill, just as the Azumarill from before appears and hides behind Trixie's legs. Totodile comes out of the bushes and blows kisses at Azumarill, but she turns her nose up at him.
Later, at a circus tent, Trixie explains that she always enjoyed the circus and has taught her Pokémon to do tricks. Lately, she has had trouble with Azumarill, who has been acting strangely ever since Golduck joined the troupe. Brock and Totodile later help set up for a show but the latter picks up Azumarill and puts her in the pool, only to be sent flying with Water Gun again. Ash doesn't understand why Totodile is acting this way, and Misty tells him that he will understand when he is older and more mature. In contrast, Brock understands Totodile's feelings immediately and encourages him to pursue Azumarill.
When the show starts, Trixie performs a magic act first as Azumarill comes on and juggles colored balls with her Water Gun. Totodile gets away from Ash and jumps up onto the stage, showing off his own water tricks with fruit tossed to him by the audience. Annoyed, Azumarill storms off, while Ash climbs onstage to try to catch Totodile, but he ends up having to catch the fruit when Totodile runs after Azumarill. Brock promptly reaches a solution to Totodile's dilemma: he will teach Totodile to be successful in love. Team Rocket peers inside the circus tent, and they plot to steal Azumarill and Pikachu so they can start their own traveling circus and get rich.
Later, Brock starts his lessons with Totodile. He hands Totodile a jar of his homemade Pokémon treats and suggests that Totodile should give them to Azumarill. Totodile does so but is rejected again. Suddenly, a net comes down, captures Azumarill, and drags her away. Totodile chases after Azumarill as Brock watches from the bushes. Brock's yelling alerts Ash and Misty to the situation and confront the culprits, Team Rocket, who recite their motto as they board their balloon. Jessie antagonizes Ash, and he orders Pikachu to use Thunderbolt. However, Meowth shoots out a net and traps Pikachu inside an electric-proof cage. Weezing's Smokescreen allows Team Rocket to escape, but Totodile runs after the departing balloon. While struggling, Azumarill loses the ribbon tied to her tail. Totodile catches it, and as Team Rocket floats away, Totodile dives into the lake and resumes the chase via water, ignoring Ash and Brock's yells to come back. They soon inform Trixie, and following Misty's suggestion, they search the forest on the other side of the lake.
As Team Rocket hides in a log cabin, Jessie and James try to persuade Azumarill to do tricks for them, but she refuses. The trio quickly gets tired of Azumarill's behavior and resorts to using force, but they are stopped by a Water Gun from Totodile, who has found them. Meowth promptly muzzles Totodile and ties him up. At nightfall, with Team Rocket asleep, Azumarill looks out the window at the moon and starts to cry. Totodile promptly gives her her ribbon back and cheers her up by dancing.
In the morning, Team Rocket prepares to leave with the new intention of giving the Pokémon to the Boss for a reward. As they lift off in their balloon, they are spotted by Trixie's Pidgey, which pokes a hole in the balloon, and they crash. The cages fall out, and Ash gets Pikachu and Totodile back, but Team Rocket is still holding onto Azumarill. Trixie orders Golduck to use Water Gun, which defeats Weezing and Arbok. Bulbasaur's Razor Leaf attack slices open the cages, and Totodile uses his Water Gun to knock Team Rocket over so that Bulbasaur can retrieve Azumarill's cage with Vine Whip. To finish them off, Pikachu's Thunderbolt sends them blasting off again.
Bulbasaur slices through the cage with its Razor Leaf flurry and frees Azumarill. Brock urges Totodile to confess his feelings for Azumarill. However, as Totodile does so, Azumarill rushes past him and instead embraces Golduck, much to everyone's surprise. Trixie finally concludes that Azumarill's odd behavior was because she was actually lovesick over Golduck. Brock comforts the disappointed Totodile, saying that love is still worth fighting for. Before the group departs, Brock flirts with Trixie one last time and has to be dragged away. Ash calls to Totodile, who is sitting on the shore of the lake watching a Quagsire. He runs to the Quagsire and dances for it but gets rejected. Ash is forced to chase after Totodile with his Lure Ball, as he tries to get him to return.