After teaching his friend to fight germ creatures, in What The Cat Knows, Thomas was last seen heading home to find his pets. Germ creatures are responsible for infecting people with disease and making them sick. Cats are the only ones that can see these creatures and cure them. Hairballs And Sticky Things tells the story of Thomas

When a small kitten (Cupcake) is brought home, her new owners (Andy and Carol) don't quite know what to make of her strange behavior. Since Andy and Carol have never had a cat, they didn't realize that all cats behave this way. As it turns out, there's more going on in the home than Andy and Carol can see. Horrible germ creatures are lurking about, trying to make people sick. Only cats can see them and its Cupcake's job to make sure she keeps these creatures from getting her family sick. The kitten attacks the germ creatures, even though she is very afraid of them. Another cat (Thomas) tries to help Cupcake find her courage. Thomas also helps Cupcake understand her feelings about the new baby that has just arrived in the home. Just as Cupcake is about to conquer her fear, an evil germ creature has come into the home and it's after the new baby