A penguin moves in. Just moments ago, the Stewart family saw the little penguin at the zoo, and now he is standing at their door. Imogen and Arthur are thrilled, but their parents are less enthusiastic. However, you can't just leave a little penguin out in the cold, so they invite him in for dinner. As it turns out, penguins also enjoy lasagna, although their table manners leave much to be desired. The next day, the little penguin is supposed to return to the London Zoo. But as it turns out, no penguin is actually missing from there. Strange! Where did the penguin come from then? Imogen and Arthur are happy that Einstein can stay for now, but they also want to solve the mystery of the little penguin.