On the way to Dawn's next contest, Ash and friends encounter a Magnezone in a forest. The Magnezone is enraged and is quickly heading for a nearby town, so Ash and the others try to stop the rampaging Pokémon before it makes it to the city.
While on the way to the next contest town, Gible falls in a river. Buizel saves it. This attracts the attention of a trainer, who wants to have a battle between Buizel and his Mr. Mime. Ash agrees. Mr. Mime proves to be too strong for Buizel though. Following this loss, Buizel is determined to get stronger and defeat Mr. Mime.
On the way to the next contest, Ash and friends meet a trainer who is training for a competition known as the Pokéathlon. Interested in what it is, they decide to go check it out. Ash then decide to enter the competition.
Contest day has finally arrived and Dawn is trying to perfect Mamoswine and Cyndaquil's "Flame-Ice" combination. However, a Plusle and Minun shows up. Dawn begins to act strangely, revealing that she has a bad experience with a Plusle and Minun in the past. Things are made worse when Dawn's mean spirited rival Ursula shows up. Ursula is ready to defeat Dawn. Can Dawn keep it together for the contest?
Dawn and Ursula have made it past the first round and must now face each other in battle. Although Mamoswine and Cyndaquil are doing great, Ursula has a secret plan for Plusle and Minun. Will Dawn be able to defeat Ursula and win her fifth and final ribbon?
On the way to Sunyshore City, Ash and friends run into Barry, who has just recently defeated the Sunyshore Gym Leader, winning a badge. Ash and Barry decide to have a battle, Empoleon vs. Monferno. During the battle Monferno's Blaze ability becomes activated and trouble begins. Meanwhile, Team Rocket is planning on stealing all of their pokémon.
Piplup is getting sick and tired of being constantly hit by Gible's failed Draco Meteor attacks. Fed up, Piplup runs away, and heads towards Professor Rowan's lab. Will Dawn be able to find her beloved Pokémon?
Ash and friends have finally arrived in Sunyshore City, where Ash will challenge the Gym Leader and try to win his eighth badge. However, something is wrong with Volkner, the Gym Leader, and he does not seem interested in battling at all. However, his friend, Flint of the Sinnoh Elite Four has an idea to rekindle his spirit.
Ash is finally going to battle Volkner, the Gym Leader of Sunyshore City so he can get his eighth badge and qualify for the Sinnoh League. However, a mysterious power outage occurs, canceling the battle. Everyone heads to Sunyshore Tower, the source of the city's power, but it has disappeared! Now they must somehow trace it and bring it back.
With Ash's Sunyshore Gym match delayed, Ash and friends head towards Lake Valor for the Grand Festival. They meet up with Dawn's mother Johanna who asks them to help out at a school. They help out, but things get hectic, especially when a kid takes a "liking" to Piplup. Dawn decides to use this time at the school to perfect some combos for the Grand Festival, while Jessie sets her sights on her fourth ribbon.
Continuing on to the Grand Festival, Ash and friends find a girl named Marley in a river and swiftly bound for a waterfall. Brock rescues her, and they find out that a legendary Shaymin is with her, injured by a group of thugs who want to steal it. Team Rocket, who are the ones responsible, set out in an attempt to nab Shaymin once more. Ash and friends, knowing the danger, join Marley in helping to keep Shaymin safe while returning it to its friends.
Ash and friends encounter a Pokémon Ranger named Ben. They find out that the legendary Heatran has been disturbed and is now going on a rampage, and Ben is on a mission to calm it down. Meanwhile, Team Rocket decide to catch Heatran, eager for the legendary Pokémon's power.
On the way to the Grand Festival at Lake Valor, Ash and friends arrive in a small town and run into a young boy who left his Magby at what was apparently a fake Daycare Center. As a result, it was stolen, so Ash and friends decide to help. After they begin their search for Magby, they encounter a woman who introduces herself as Bertha, and who also seems to know how to find Magby. While Ash and Dawn don't see it themselves, Brock realizes who Bertha is. What is Bertha's secret?
Ash and friends arrive in a town where they find out that one of the last contests before the Grand Festival is going to be held. Since Dawn already has her fifth ribbon, however, she decides not to participate. As they're moving on, a woman comes up to them and asks them to follow, bringing them to a princess by the name of Salvia. Surprisingly, Salvia looks as if she could be Dawn's identical twin, and because of this, the former asks Dawn if she could take her place as princess for one day so that she could participate in the Pokémon Contest. How will Dawn react to this extraordinary request?
With the Grand Festival coming up soon, Dawn begins to train with her new Togekiss. Togekiss likes to move as elegantly as possible when performing a move in battle which causes confusion. Meanwhile, Jessie decides that Togekiss is perfect for her, and sets her sights on catching it.
Ash and friends finally arrive at Valor Lakefront, site of the Grand Festival. Trouble ensues, however, when they encounter a girl named Makina, dressed up as Flint of the Elite Four, and owner of two Ditto; one of alternate coloration. Despite the fact that she's only been a trainer for a month, Makina mocks Ash for being a "newbie", and loudly proclaims that regular trainers and Gym Leaders alike would run in fear from her two Ditto (which is her reason for not having any gym badges). When battling Ash, however, Makina's tough facade starts to break, and she shows that she's not exactly as "all-powerful" and as she claims.
Ash and friends return to Lake Valor where the Grand Festival is to begin shortly. Dawn reunites with her rivals and gets ready for the first round. The first round is a double performance, and Dawn chooses Buneary and Cyndaquil. Will she make it past the first round?
The Grand Festival continues and Dawn and her rivals have made it past the appeals round, and have moved on to the battle rounds. Dawn's first opponent is Ursula, who decides to use Gabite and and her newly evolved Flareon. Along with Mamoswine and Pachirisu, will Dawn be able to defeat Ursula and progress to the Top 16 round?
As the Grand Festival rages on, Dawn, Zoey, Nando, and Jessie battle their way past tons of talented coordinators and the four of them arrive in the Top 4. The first battle is Zoey vs. Nando. Nando chooses Kricketune and his new Lopunny while Zoey goes with Leafeon and her newly evolved Mismagius. As the battle goes on, both trainers put on an amazing battle, with neither giving an inch. Later, Dawn and Jessie take the stage for their battle. Which two coordinators will advance to the final stage and battle for the Ribbon Cup?
The final round of the Grand Festival has arrived. As they promised long ago, Dawn and Zoey are the final two contestants. As the battle begins, Zoey chooses her Glameow and her newly evolved Gallade, while Dawn goes with Piplup and Togekiss. With only one battle standing between them and the Ribbon Cup the battle is sure to be fierce, but who will ultimately win?
With the Grand Festival over, Ash and friends begin to head back to Sunyshore City. Team Rocket is once again in pursuit, but their plans are put on hold when Meowth falls in love with another Pokémon. Now he must choose whether or not to follow his new love, or stay with Jessie and James.
Ash and friends return to Sunyshore City and Ash is excited to finally get the chance to battle Volkner to try and win his eighth and final badge. Will Ash be able to defeat Volkner and finally be able to qualify for the Sinnoh League?
Ash and friends run into Kenny who is having a special training session with Olivine Gym Leader Jasmine. Kenny is already preparing for the next Grand Festival, and this worries Dawn as she has not decided what her next step will be. Kenny challenges Ash to a battle and says that if he defeats him, then Dawn must travel with him. Who will win the battle?
Ash and friends board a ship which will take them to the location of the Sinnoh League. On the boat they meet a trainer named Buck. They decide to help him find a treasure which is said to be located on a nearby island.
It is almost time for the Sinnoh League competition to start. Knowing that the Sinnoh League is going to be tough with rivals like Barry and Paul competing, Ash decides it is best if he uses Pokémon not only from his Sinnoh journey, but all his other past journeys as well. However, which ones will he choose.
The first round of the Sinnoh League begins. Ash's first opponent is Nando. Sending out Staraptor against Nando's Roserade, he thinks he has a good advantage. However, Nando is no push over and begins to take the lead. Will Ash be able to defeat Nando, the trainer who fought grandly in the Grand Festival?
The third round of the Lily of the Valley Conference is about to start. Much to his happiness, Barry's next match will be against Paul, a trainer he looks up too. As the battle begins Paul believes it will be an easy win, but Barry soon proves that he is no pushover. Which trainer will advance to the next round?
The Sinnoh League continues and it is time for Ash's battle. Ash will be going up against Conway. As the battle begins Ash gets in over his head when Conway uses the move Trick Room, changing the battle. Will Ash be able to defeat Conway and progress in the tournament.
After defeating Conway, Ash has now progressed to the Top 8 in the Sinnoh League, and it's finally time for him to go up against Paul in the Sinnoh League battle promised after Monferno's evolution. With the return of Gliscor, Ash decides to use the same Pokémon he used in his full battle with Paul at Lake Acuity, determined to show that they have grown considerably since then. The time has come; will Ash finally be able to defeat the rival he made when he first set foot in the Sinnoh Region, and progress even further in the tournament?
Ash and Paul's battle in the Sinnoh League quarter-finals rages on. Things are looking good for Ash, who has so far defeated Paul's Aggron and Gastrodon and still has all of his Pokémon remaining, but the tables start to turn when Paul sends out his new Drapion. Will Ash be able to hold his ground and defeat his Sinnoh Region rival once and for all?
Ash and Paul's battle in the Sinnoh League quarter-finals rages on as both trainers give it their all. Eventually, both Ash and Paul have just one Pokémon remaining; Infernape for Ash and Electivire for Paul. Which trainer will emerge victorious in this decisive battle and move on to the semi-finals?
Ash has defeated Paul and advanced to the semi-finals of the Sinnoh League. Ash's biggest challenge, however, is now ahead of him. His next opponent is Tobias, who has won his eight badges and advanced to the semi-finals of the tournament using solely his Darkrai. Will Ash be able to defeat Darkrai, as well as Tobias's other Pokémon, and advance to the finals?
With the Sinnoh League behind them, Ash and friends take a ship back to Dawn's hometown of Twinleaf. A crisis emerges, however, when a group of Tentacruel attack the ship and poison many of the Pokémon on board. With no other doctor on the ship, Brock is the only one who can help those Pokémon. Will he succeed before it's too late?
Back in Twinleaf Town, Ash, Dawn, and Brock finally come to realize that their journey together is over. Everyone is sad about this, especially Piplup who is overwhelmed with tears. However, as one journey ends, one is also set to begin.