On a rainy night at the Magic Express, Ace and Cosmo are ready for dinner with Mona when they get an unexpected surprise on their doorstep: a baby. Cosmo tries to take care of the baby while Ace looks for the person left the baby in the rain. Mona demonstrates Cosmo on babysitting since she's better and Cosmo not good at it. During the night though, Ace decided to name the baby, Junior. However through the night, Mona is shocked that the baby has grown into a toddler. Angel analyzes the child who grows older each hour. Junior then takes the Magic Rider like a maniac and starts causing all kinds of trouble. Ace and Mona catched with the Racer via the Magic Bike, but Junior has used the ejector seat and ends up at the top of a high-rise building. Ace and nearly lost Junior when a strange man picks him up in a turbocopter. The man, Aldus Teron, is up to no good so Ace rescues Junior when jumps from Teron and gets into a very high dive with Ace. Teron goes back to Ingen Laboratories and le