Black and White 3-
Five years after the events of Black and White 2, you are a boy/girl from Accumula Town. In these five years, Drayden and Alder have passed away, two Universities are founded in Striaton and Aspertia, Castelia City has fallen into total economic collapse, Nimbasa's attractions have closed down, and the Marine Tube has cracked. On a routine stroll to Nuvema Town, you see Colress talking with two red-headed men. The people off at P2 Labaratory have been salvaging technology from all over the world, and have developed a makeshift Pokedex that now needs testing and filling. You eventually get said Pokedex, and Colress provides you with a Pokemon to fill said Pokedex.
Taking advantage of the terrible economy of Castelia City, Team Rocket has risen back up in a fashion similar to that of the gangs of the American Prohibition era, under a new leader. As a result, Castelia City becomes the largest hideout in Pokemon history. Being near the Desert Resort, they plan to take everything within it and sell it for a profit, including the Pokemon. The Gym Leaders are powerless against Team Rocket's empire, and the only person that can fight them is -obvious plot-.
Gameplay wise, you head to Castelia via the only route available (through Nacrene and Striaton) then progress around the Unova "loop".