After Holly's mom has twin boys, Holly realizes that cats are no trouble at all in comparison. Now the boys are on the eve of their second birthday, and Holly's mom and stepdad are too pooped to put on a party. Holly to the rescue! With help from her best pals, Holly plans everything right down to cake, balloons and entertainment – but she doesn't count on a lost pet cricket, an exploding espresso pot, or those always unpredictable cats. You won't want to miss the funniest birthday party.
Holly's back, and so are those cats! This time Mom and William have made her move to a new house, and the neighbors are really weird. What is that silver machine in the backyard next door anyway? Is the boy who built it really a mad scientist? And what has he done with George Cat?
Holly's late to school. She forgets her homework. The kids don't like her. What's the trouble? Cats! Now that Mom has married William, Holly has to share a room with four troublesome cats. Holly doesn't like the cats. And they don't like her – or do they?