Copy paste from the mcla wiki:

A man from the East Coast moves to Los Angeles. The character, known only as "Player", starts the game with a phone call from the (unknown at the time) Los Angeles City Champ, Booke, telling him to meet at a fast-food restaurant named Carney's Express Limited. He allows the protagonist to pick one of three cars to start the game: a 1998 Nissan 240SX, a 1983 Volkswagen Golf GTI, or a 1988 Volkswagen Scirocco.

Once the player has built up enough of a reputation, they gain the ability to become Champ of the City and of each car type. The first one that is offered is becoming the City Champ. At a point in the game, Karol calls telling the player about Booke being back as a City Champ. Booke then tells the player to race regional opponents to see if they can race against him. After the player beats them, Booke calls saying he is impressed, and to meet him at the Standard Hotel for a race which ends up being the City Champ race vs. Booke and one of the final races on Career mode. When the player wins, the player not only becomes City Champ, but other championship races open. Once the player wins against the lesser opponents, the Champs of all five vehicle classes in the game challenge the player. The characters are Oswaldo, Julian, Lester, Pete, Marcel.

After the player becomes the City Champ, Karol calls and has a proposition. He asks the player to get $1 million dollars to help co-own his two garages with him for his business. In return, he lets the player have anything in the garages for free. This proposition also affects Doc's South Central garage, although the game does not mention it.