The boys are back in [Pallet] Town! But they quickly discover their that mom and Professor Oak aren't impressed. They head north to discover Giovanni, of Team Rocket, is the eighth Gym Leader—and, of course, defeat him for the last time. With the Earth Badge, they then head west and humiliate their rivals before heading up Routes 22 & 23 and venture into Victory Road on their way to the Elite Four.
Notes: Check out "Dr. Lava's Lost Pokémon" on Twitter @DrLavaYT, whose tweets helped inform the lore in this episode.