Kate and Dad are building derby cars to race on their homemade track. In Mimiloo, Kate, Mim-Mim and all their friends race their own cars in the Rip Roaring Race at the Rumbly Race Track. In everyone's haste to win, Mim-Mim is the only one who tested his car beforehand. Lucky for his friends, Mim-Mim added some special parts!