Ash begins his journey in Johto, a largely unexplored region said to be thickly populated with Pokémon entirely new to him and his friends. After they briefly encountered a legendary Pokemon, Suicune, Ash and his friends arrive at New Bark Town to register for the Johto League. However, one of the three Johto starter Pokemon, Totodile, has been stolen by Team Rocket from Professor Elm's laboratory (and it chomped on Jessie's hair). Will Ash save the Totodile? And will he get to register for the Johto League?
The air date between the Japanese and English versions of this episode were exactly one year apart.
It can be assumed that Cyndaquil was given to Jimmy and Totodile was given to Marina, as pointed out in the Pokémon Chronicles special: Raikou, the Legend of Thunder.
Professor Elm assumes that Ash must be from Pallet Town based solely on the Starter Pokemon he mentioned, but it is unlikely that all new trainers in Kanto start there. Brock and Misty clearly did not as they had not been there before Ash's return before the Indigo League, and Brock's starter was Onix, which is not available from Professor Oak anyway.
Although the Generation II Pokemon that will be encountered in Johto had not been invented when the anime started, it seems odd that, from an in-universe perspective at least, Ash and co. would always refer to there only being 150 Pokemon (excluding individual Pokemon such as Togepi and Marill), when Johto is only a few days walk from Pallet Town and is hardly an isolated continent. Even Professor Oak, who briefed Ash on the Johto League, seemed ignorant of Pokemon outside of Kanto at times despite being in contact with people such as Kurt in the Johto region.
The "Who's that Pokémon?" in this episode is Chikorita.
In the Indigo League, Ash had to get all 8 badges before he could register. At Johto, he was able to register right away.