Evan Treski is people smart. He’s good at talking to people, even grown-ups. His younger sister, Jessie, on the other hand, is math smart–but not especially good at understanding people. She knows that feelings are her weakest subject. With just five days left of summer vacation, Evan and Jessie launch an all-out war to see who can sell the most lemonade before school starts. As the battleground heats up, there really is no telling who will win–and, even more important, if their fight will ever end.