After May's first Pokémon Contest in Slateport City, Ash, Brock, May and Max decide to stay in the city one more day. Brock decides to go shopping to stock up on supplies, and May goes with him. Ash and Max rather make their way to Oceanic Museum, but to their surprise they find that it is closed. Ash consults the guide book, but Max is not ready to give up on the visit so he tries to climb the museum wall. Before he could climb, a boy named Marius confronts him thinking that Max wants to steal museum's exhibits. Ash comes to see what's going on, but Marius calls him a thief too and sends out his Spheal, commanding him to use Water Gun. Spheal disobeys and attacks Marius instead. Marius then commands Spheal to use Body Slam. Ash and Max dodge the attack, Spheal bounces off a wall and ends up knocking Marius down on the ground. Marius orders his Spheal to use Blizzard and Ash tells Pikachu to counter Blizzard with Thunderbolt. Spheal is easily knocked out, what surprises Marius. Max explains him that Water-type Pokémon have a weakness to Electric-type moves. Ash advises Marius to return Spheal to its Poké Ball so that Spheal can rest.
Captain Stern, the curator of the museum then comes, and Ash and Max explain to him that they weren't trying to steal museum's property. After Marius's apology, Captain Stern explains that he had to close the museum because of an unexpected event, but invites Ash, Max and Marius to come to the museum anyway. Jessie, James and Meowth observe the scene from hiding and make a plan to steal Ash's Pikachu and then rob the museum. Ash, Max and Marius admire the Oceanic museum's exhibits. Marius tells him that his dream is to become a scientist and travel the sea in the submarine that Captain Stern is currently building.
Captain then takes the three to his office to explain why has he closed the museum: he received a sample of an unusual dark rock from the bottom of the ocean that underwent extremely high temperatures. Ash and Max are astonished because they cannot understand how can there be heat at the bottom of the ocean, but Captain Stern tells them that it may be work of a Pokémon. Just when he finished explaining, Team Rocket's voice is heard from the museum's courtyard and they appear to be selling snow cones. Ash, Max and Marius go outside to buy it, while Captain Stern stays in the museum.
Ash, Max and Marius are enjoying their icy desserts, when it occurs to Max the museum is closed and the snow cones salesmen ought to know that. However, Team Rocket persuades them to continue eating. When the three are almost unable to move due to freezing effects of snow cones, Team Rocket reveals their true identity and steals Ash's Pikachu, putting him in a metal cage, and traps the three boys in another metal cage too.
Meanwhile, three Team Magma members including Tabitha break into the building and steal the curious stone. Captain Stern confronts them, but Tabitha distracts him with his Mightyena's Shadow Ball to escape. Team Magma members are now running out of the building. Team Rocket spots them and figures that whatever it is that Team Magma is stealing must be valuable, so they decide to steal it from them. Marius tries to break the cage using his Spheal's Body Slam, but he disobeys again. Ash commands Corphish to break the cage with Crabhammer.
Team Rocket blocks Team Magma's way by sending out Seviper and Cacnea. Jessie commands her Seviper to use Poison Tail but Tabitha's Mightyena tackles it. James tells his Cacnea to use Pin Missile, but Mightyena uses Double Team to raise its evasion, making Cacnea's attack miss. Seviper tries to use Wrap, but Mightyena's Iron Tail hits first, sending Seviper flying into Team Rocket who then blasts off, dropping Pikachu's cage. Cage falls on the ground and opens.
Ash, Max, Marius then arrive with Captain Stern running behind them. He sends out his Sealeo and attacks Mightyena with Aurora Beam. Mightyena dodges and the beam hits the ground, exploding. Explosion blasts Mightyena off right into Tabitha causing him to drop the stone case. Marius catches it and hands it over to Captain Stern. Other two members of Team Magma send out their Mightyena. Meanwhile, Brock and May are done with their shopping and decide to come to the museum.
Ash sends out his Corphish and Pikachu to battle against Mightyena alongside Sealeo. Captain Stern tells Max and Marius to run into town to get Officer Jenny when the time will be suitable. All three Mightyena use Hyper Beam while Corphish, Pikachu and Sealeo use BubbleBeam, Thunderbolt and Aurora Beam, respectively. The attacks collide, causing an explosion. Smoke covers the area, so Max and Marius start to run. The boys have to escape the scene fast, so Marius decides to jump off a cliff into the sea. Max is terrified and does not want to jump. Tabitha orders Mightyena to use Shadow Ball, so Marius takes Max's hand and drags him down to dodge it. The two boys and Spheal slide down the cliff and end up in sea. They hold onto Spheal who starts swimming to the city. Max and Marius meet May and Brock who are just making their way to the museum.
Meanwhile, Captain Stern hands the stone case to Ash, telling him to run while Sealeo distracts them using Blizzard. Ash runs with Pikachu and Corphish, but despite Blizzard, Mightyena uses Shadow Ball and hits ground in front of Ash. The explosion sends Ash flying. While in the air, Ash drops the case. The case opens and the stone falls on ground and splits into two pieces, one being significantly bigger than the other. Pikachu runs to save the stone, but Mightyena gets there first, steals the bigger part of the stone and gives it to Tabitha. Team Magma's helicopter arrives and Mightyena uses Shadow Ball to distract Captain Stern and Ash while Team Magma is getting aboard. As Ash and Captain Stern watch the helicopter furthering away, the police arrives along with Brock, May, Max and Marius.
Ash apologizes to Captain Stern for dropping the stone, but Captain Stern tells him it doesn't matter because he retrieved the smaller part of the stone which will be sufficient for his research. Ash, Brock, May and Max then bid their farewells to Captain Stern and Marius as they hit the road again to travel to Mauville City.
- Featured Pokémon: Nuzleaf
- Team Magma uses the object much later to get Groudon.
- This episode's title is a reference to the term "seal of approval".
- After this episode, Pokémon underwent a nearly three-month hiatus on Kids' WB!, and did not return with new episodes until September, despite the new season not beginning until What You Seed is What You Get.
- The hint given in the Who's That Pokémon? eyecatch, "This Pokémon lives in in the forest and enjoys startling people!", has an extra in.
- In the Hungarian dub, a Team Magma Member asks his Mightyena to use "Shadow Bell" instead of "Shadow Ball".
- While Ash, Max, and Marius are eating snow cones Ash and Marius' snow cones trade colors. Ash's snow cone became yellow, and Marius' became green. This was corrected the next time the cones were shown.