Penelope Rex has one fear: Walter, the class goldfish. So when Mrs. Noodleman tells the kids that they'll be taking turns bringing Walter home, Penelope gets carried away by her anxious imagination. The weekend has a rocky start - from Walter ominously licking his lips to a sleepless night where the fish's bowl appears to move closer and closer to Penelope's bed. But then Walter goes missing! Penelope must face her fear to find him and realises along the way that there's more to Walter than his chomping jaws.