Pokémon : S5 | E26 – Talkin’ ‘Bout an Evolution (1)

Ash and his friends are walking near Mahogany Town when all of a sudden Pikachu feels sick, followed by Togepi. Brock looks at the surroundings and declares that they must be lost. Several Bug Pokémon suddenly drop down from the trees, which frightens Misty, but they appear sick too. As they wonder what is happening, a large roar attracts their attention. The group reaches the banks of the Lake of Rage. All of a sudden a Red Gyarados appears from the water, startling everyone. Within moments of its appearance, Gyarados fires out a Hydro Pump towards the group, which misses. Ash and the others conclude that Gyarados must be sick as well, so they decide to leave the area.

The group is halted by some members of Team Rocket. Tyson doesn't want his plans ruined and he sends out a Fearow to take care of them. Ash calls on Totodile, though he is unable to attack because of a wave of weakness that hits. Fearow is seemingly unaffected. It dives in with a Drill Peck, but a Thunder Wave strikes it down first. A Dragonite and its Trainer arrives on the scene. He orders Ash and the others to move away, and the group follows orders. Tyson and his Team Rocket Grunts go to pursue them, but Dragonite delivers a powerful Whirlwind to keep them at bay. The Trainer flies off on his Dragonite and meets up with Ash's group in the forest. Misty notices that the man seems familiar, and the group quickly recognizes him as Lance, the Pokémon League Champion. The Trainer confirms that he is Lance and reveals that he is part of the Pokémon G-Men, a detective organization that seeks to catch people misusing Pokémon. Lance mentions that the Red Gyarados has something to do with Team Rocket’s latest operation at the Lake of Rage. Ash is keen to assist, which Lance politely declines. He explains that it would be too dangerous for Ash, especially since the Team Rocket members are no ordinary grunts. Lance directs them to a path that will lead to Mahogany Town and wishes them all the best.
(Source: Bulbapedia)