Lois finds mysterious pee stains on the floor and thinks that it is time to potty-train Stewie. Stewie says he is not responsible for the pee stains and won't allow anyone to train him. Brian secretly knows that he is the culprit. His secret is found out at the grocery store and Brian is sent to the a therapist who suggests Brian takes a vacation in Europe. Brian realizes that the reason for his pee-stains is his love for Louis.