One of George's favorite things to do in the city is visit Mabel's Department Store, because there are so many things to do. One day while The Man With the Yellow Hat is doing his shopping George sees something he never has before, a moving light in the shape of a train, and soon discovers that a lamp with a rotating shade is making it. Fascinated by the light, George decides to make his own moving light for home, but when he stays at the store too long to find out how he winds up locked in after hours. With nothing else to do, George decides to make his own moving light right in the store.