Obi the gerbil must fend for herself in a dangerous household, consisting of a dog, three cats, a parrot, and a mouse hidden in the attic, when the Armstrongs go on vacation and instructions for taking care of Obi get lost.
When pet gerbil Obi's owner Rachel gets a new puppy, Obi is jealous, but when the puppy runs away it is up to Obi to brave the dangers of the outside world and bring the new pet home.
Hugo can have the gerbil he wants, but only if he can first endure the boredom of spending seven hours--the length of time he is at school each day--in a nearly-empty room to learn how a caged animal feels.