Ash and friends discover a red Gyarados, unknowingly uncovering a plot by Team Rocket to control the secrets of Pokémon evolution. To ensure their silence, Team Rocket attempts to capture the children, but is foiled by a member of an elite Pokémon defense organization, who releases the children with instructions to continue on their way and leave the dangerous job of ending this Team Rocket experiment to adults like himself. Ash and friends assent at first, but before long, unable to ignore the compassion he feels for the red Gyarados that seemed to be in such pain, Ash decides to return and lend a hand.
S5 | Episode 22
Dues and Don'ts