En route to Ecruteak City, Ash is afflicted with a stomachache, caused by some overeating earlier. With no medicine to treat it, Ash and his friends are greeted by Old Man Shuckle, a pharmacist. The old man gives Ash some pills, which he takes, resulting in an explosion of purple gas from his mouth. Misty gets angry and yells at Old Man Shuckle when he tells her that the pills he gave Ash are Pokémon medicine. When Ash recovers, though, he reports that his stomachache is now gone, and Misty calms down. Old Man Shuckle explains that his medicine works on both humans and Pokémon, and Brock is excited to discover that he makes the medicine himself, quickly taking the old man up his offer to show him where the medicine is made.
Old Man Shuckle reveals his laboratory, packed with natural ingredients, but admits that there is a special secret to how his medicine is produced. He shows the group a storeroom, full of strange red containers with corks in them. Misty picks one up and is surprised to find that the containers are actually Shuckle. The old man explains that he fills the Shuckle shells with his ingredients until they turn into the juices that form the basis of all of his medicines. Different ingredients and Shuckle produce different medicines, and he shows the group a picture of a rare purple Shuckle, which can produce a juice that would allow its user to tame any Pokémon. Brock is extremely taken by this notion and asks the old man for some of the juice. However, Old Man Shuckle says that tracking down a purple Shuckle isn't easy, although if he had help in finding it, he would be willing to share the juice. He introduces the group to Spoopy, a Bellsprout that checks the scent of Shuckle in order to see if the juice inside them is ready.
When out looking for Shuckle with Spoopy, Old Man Shuckle explains that only wild Shuckle can produce quality juice, and so instead of catching them, he simply takes them back to his laboratory, fills them with ingredients, and returns them to the wild for a year while the ingredients turn into juice. Spoopy then detects the Shuckle by scent, and they are returned to the laboratory. Despite Spoopy's help, finding the Shuckle is still an arduous process, and so Ash and friends agree to help. Nearby, Team Rocket is listening in, excited at the prospect of a juice that would make any Pokémon obedient to them.
Ash, Brock, and Misty struggle to keep up with Spoopy as it checks Shuckle throughout the forest. Suddenly, Spoopy charges off, excited, and Brock gives chase, believing it has picked up the scent of the purple Shuckle. He fails to keep up with the quick-footed Bellsprout, however. Spoopy lifts up a rock and finds a purple Shuckle underneath it. Shortly afterwards, the group catches up, finding Spoopy and the purple Shuckle deep in conversation. Before they can reach them, though, Team Rocket descends from the trees and recites their motto. Jessie grabs the Shuckle, while James's Weezing uses a Smokescreen to cover their escape. When the smoke clears, Team Rocket has gone, but Spoopy still has the Shuckle's scent, and the group pursues them.
Meanwhile, Team Rocket is out of breath and thirsty. Realizing they have the Shuckle juice, they decide that one of them should try it to check if it is safe. Meowth finds himself volunteered to test it, and when it seems to have no adverse effects, Jessie and James drink it too. The three enjoy the taste and start to fight over the remaining supply.
Spoopy leads the group to a river, apparently a dead end. Suddenly, many Shuckle begin emerging from the bushes, all heading in the same direction. Old Man Shuckle arrives and concludes that somebody must have drunk the purple Shuckle juice, thus attracting the other Shuckle. Knowing that the Shuckle will lead them to Team Rocket, the group follows them. Meanwhile, Jessie and James are feeling a little lightheaded from drinking the juice. Meowth suddenly displays some very unexpected behavior, declaring his love to an astonished James.
Following the Shuckle, Old Man Shuckle says that drinking the undiluted purple Shuckle juice would cause a human to emit strong pheromones that would attract any nearby Pokémon for three days. This seems to be coming true for Team Rocket. While Meowth obsessively licks James's face, Jessie discovers an amorous Shuckle licking her hand. Soon, they realize they are surrounded by lovestruck Shuckle, and flee, directly into the path of Ash and friends. Brock tells them that Meowth and the Shuckle's behavior is a result of drinking the undiluted juice. Despite this Team Rocket refuses to hand over the purple Shuckle. Jessie sends out Arbok and Wobbuffet to battle, but both fall under the effect of the pheromones and pounce on her. James tries to help her by sending out Victreebel, but it affectionately tries to eat him as usual. Team Rocket recalls their Pokémon and concedes defeat, but Pikachu stops listening to Ash and approaches Jessie, lovestruck. Deciding that things have gone too far, Old Man Shuckle scatters some powder over the area, neutralizing the effects of the pheromones. Meowth and the Shuckle return to normal, although Jessie still has hold of both Pikachu and the purple Shuckle. The purple Shuckle emerges from its shell and licks Jessie's navel, causing her to fling it into the air in shock. Spoopy uses its Vine Whip to catch it. Jessie boasts that she still has Pikachu, although she soon discovers that Pikachu is no longer affected by the pheromones either, and Team Rocket is quickly sent blasting off.
Back at his laboratory, Old Man Shuckle thanks the group for helping him obtain more Shuckle juice than ever before. He presents Brock with some Pokémon-taming medicine, as promised, but Brock decides to decline. Having seen how the Shuckle flocked to Team Rocket in spite of their nature, he says he would prefer to tame Pokémon the normal way. The friends bid Old Man Shuckle goodbye and continue on their journey. Meanwhile, Team Rocket is hiding in the bushes from a swarm of amorous Beedrill and multiple Ursaring, noting that when the effects wear off after three days, they will probably attack.