Little sister Annie and big brother Simon are (mostly) good friends, but even friends disagree sometimes. Annie is pretty convinced that their banana-muffin batter is lacking a certain crucial chocolatey ingredient, but all Simon can do is grumble about following the recipe. And when Annie unearths some precious items from her babyhood, Simon tells her she's way too old to walk around with a pacifier in her mouth. But when baby Theo from next door loses his favorite toy, Annie, Simon, and even Hazel the dog prove once again that this little sister and big, big brother make a (mostly) terrific team. Returning for a third warm and wryly funny early chapter book, Annie and Simon are a testament to the fact that there isn't just one formula for the perfect family.