A yellow taxi named John (voiced by Daws Butler), along with his wife Mary (a blue taxi car, voiced by June Foray), awaits the arrival of their new son, who looks just like John.
Within his first few months, Junior is fed, changed, learns to "walk", gets his first "tooth" (a spark plug), etc.
Fed up with his father's refusal to accept his choice, Junior angrily sneaks out the window, fuels up with high octane gas, and goes zooming all around town, spooking everything in his way.
Upon seeing Junior escaping, John chases after him, but can't seem to catch him because of the octane gas.
However, John gets his second wind when he sees Junior racing alongside a train, playing chicken with it.