After a strange victory in the second round of Hearthome City's tag battle tournament, Paul has abandoned his Chimchar and Ash wants Chimchar to join his team instead. Team Rocket wants Chimchar's power for themselves, and they swoop in to steal it. Their hot air balloon getaway flames out when Chimchar toasts their balloon and happily returns to Ash. For the quarterfinals of the tournament, Chimchar will rest and watch Ash and Paul use Staravia and Torterra to battle Brock and his tag battle partner Holly, who are using Croagunk and Farfetch'd.
Unlike Ash and Paul, who are getting along just as badly as ever, Brock and Holly work well as a team. But against a powerhouse Pokémon like Torterra, even Brock and Holly are unable to win. Paul sneers at Ash for celebrating and thinks his Torterra was the only reason they won, but it doesn't matter now. Ash and Paul move on to face Dawn and her partner Conway in the final round. And for this battle, Ash chooses Chimchar and Paul chooses Elekid to battle against Dawn's Buizel and Conway's Heracross.
Dawn and Conway are good partners, too: they know how to work together and synchronize attack and defense. However, Conway's strategies didn't anticipate that Paul's Elekid would evolve into Electabuzz in the middle of the match! Buizel and Heracross do their best, but Electabuzz's power and Chimchar's Fire-type attacks win the day. Of course, now that he's evolved his Elekid, Paul couldn't care less about victory or the Soothe Bell prize. But Ash believes Paul's Chimchar will be a great addition to his team, and he's looking forward to the next Gym battle in Veilstone City!
Ash is kneeling down to the Chimchar that Paul released moments earlier. Impressed by the way Chimchar always gives it his all in battle, Ash would be thrilled to have him on his team. However, a disgusted Paul tells them that they deserve the worst and have found it in each other. Ash diverts any and all attention away from him, and assures Chimchar that, if he accepts his offer, they will both prove Paul wrong. Paul then walks away, and Chimchar takes on a glowing expression and reaches to accept Ash's offer, just when they are suddenly attacked by Bullet Seed and Pin Missile. In all the chaos, Chimchar is seized by the attackers, revealed to be Team Rocket. After finishing their motto, James tells Carnivine and Cacnea to attack Ash, Dawn and Brock so he, Jessie and Meowth can escape. However, Chimchar takes action and uses Flamethrower to destroy Team Rocket's balloon, causing it to plummet to the ground. Ash manages to catch Chimchar just in time, and with the day saved, he asks again if Chimchar would like to join his team. Chimchar happily agrees, so Ash throws a Poké Ball into the air. Chimchar happily jumps up and smacks the button, and without any struggle, Ash catches him. Later that night, Ash contacts Professor Oak to tell him about what has been going on. Although Oak is glad that Chimchar is with Ash now, he states that the situation has not changed; Ash and Paul still need to work as a team if they are to win the tournament.
The next morning, the battles continue in the Tag Battle Competition. Dawn and Conway have already won their semifinal match, so the next match-up is Ash and Paul versus Brock and Holly. Ash sends out Chimchar to watch, before sending out Staravia to battle. Paul chooses Torterra, Brock chooses Croagunk, and Holly chooses Farfetch'd. Ash makes the first move and commands Staravia to use Aerial Ace on Croagunk, who Brock commands to counter with Poison Jab. Holly has Farfetch'd launch an Air Slash at Torterra, who Paul commands to use Hyper Beam. Hyper Beam decimates the Air Slash and instantly knocks Farfetch'd out on impact, grazing Staravia in the process. Ash scolds Paul for harming his Pokémon again, before Holly apologizes for letting Brock down. He tells her not to blame herself, before telling Croagunk to use Brick Break on Torterra, who is immobilized due to Hyper Beam's secondary effect. Ash tells Staravia to use another Aerial Ace, trying to catch Croagunk off-guard. However, Croagunk slides under Torterra, forcing Staravia to stop his attack. Croagunk jumps out from behind Torterra and lands Brick Break on its head. Croagunk tries to follow up with Poison Jab, leading Ash to command Staravia to stop him, but Paul angrily tells him to let him handle this himself. He then commands Torterra, now being able to move again, to use Leaf Storm before Croagunk can use his move, which knocks him out in one shot and gives Ash and Paul victory and entry into the final round. Ash congratulates Staravia on a good job, only for Paul to comment that Staravia contributed nothing to the battle, before casting a glare at his former Chimchar, who turns away in intimidation.
Returning to the Pokémon Center after the match, Nurse Joy tells Brock that Holly was so upset about losing that she left to go and train. Devastated by losing the one woman who liked him, Brock tells Ash that he has to win the tournament. Finally, the final battle of Dawn and Conway versus Ash and Paul begins. Ash sends out Chimchar before Paul sends out Elekid, and Dawn sends out Buizel as Conway sends out Heracross. Ash and Paul take charge as Chimchar launches a Flamethrower at Heracross while Elekid readies a Thunder for Buizel. However, Buizel is able to neutralize Flamethrower with Aqua Jet and hit Chimchar, and Heracross takes Elekid's Thunder to power up his Revenge attack, which hits Elekid hard. Ash then tells Paul that they will lose if they do not start working as a team, though Paul doesn't seem to care now that his purpose for even entering the tournament in the first place has been thrown out the window. Ash then has Chimchar use Dig, which worries Dawn, but Conway tells her that now is the perfect time to unleash the strategy that they came up with for Paul's Elekid. Dawn then has Buizel rush toward Elekid with Aqua Jet, provoking Paul to have it use Protect. However, this is just what Dawn and Conway wanted Paul to do; Buizel then jumps, and Heracross comes in with a Feint attack, which shocks Paul. The Feint destroys Elekid's Protect and causes it a good amount of damage. Buizel continues the assault by hitting Elekid with Water Gun, but to his surprise, Chimchar resurfaces right below him and nails Dig. Buizel then fires right back with another Aqua Jet, causing Chimchar super-effective damage. However, he quickly recovers and his flame reignites, and Ash has him launch a Flamethrower toward Heracross, but Buizel jumps in front of Heracross and uses Water Gun. The attacks collide and cause a steamy explosion, which Elekid jumps through with a Thunder Punch in tow. Conway has Heracross counter with Megahorn, creating another explosion that sends both of them reeling back.
Elekid has taken a lot of damage at this point and Chimchar looks worried for it, but Elekid shrugs him off and begins to evolve, shocking everyone and elating Paul. The evolution finishes, and Paul commands his newly-evolved Electabuzz to charge Thunder. Conway tells Heracross to get the jump on Electabuzz with Megahorn as Dawn tells Buizel to use Water Gun on Chimchar, but Ash tells Chimchar to dodge Water Gun and use Flamethrower on Heracross, right before Electabuzz launches Thunder at Buizel. Both Pokémon are sent flying back from the super-effective attacks, and the zapped Buizel crashes into the flaming Heracross, causing a huge explosion. Just when it seems like the battle is over, the smoke clears to reveal Buizel and Heracross still standing. However, they collapse and faint moments later, making Ash and Paul the winners of the Hearthome City Tag Battle Competition. Ash congratulates Chimchar and tells Paul that Electabuzz's sudden evolution made all the difference. However, Paul remarks that Electabuzz was the only reason they won, saying that Chimchar's Flamethrower should've knocked Heracross right out, yet he still managed to stand back up. However, Ash doesn't care what Paul thinks; as far as he's concerned, Chimchar did a fantastic job.
At the awards ceremony, Enta gets on stage to give Ash and Paul their Soothe Bells. Everyone applauds Ash and Paul, while Conway muses about how ironic it is that the team that cooperated the least ended up winning a tournament that was supposed to emphasize teamwork between Trainers. That evening, at the Pokémon Center, Dawn is discouraged about losing, but promises to win her next Contest. Suddenly, Paul passes by and throws his Soothe Bell at Ash, saying he has no need for it, before leaving. Brock notes that for Paul, the tournament was simply an opportunity to power up his Pokémon, and as far as he's concerned, Elekid's evolution was the only good thing to come out of it. Conway then suggests to Ash that, since the Hearthome Gym is currently closed, he could head for Veilstone City, since it is the closest city with a Gym. The gang agrees that this is a good idea, and, with a new Pokémon on his team, Ash prepares to head to Veilstone City and earn his third Gym Badge.