The Lemonade War by Jacqueline Davies directly addresses the complex relationship between brothers and sisters, as well as how arguments can spiral out of control when people quit communicating with one another.

As the story opens, Evan Treski has a problem that involves his sister. She’s been promoted ahead an extra grade and will be in the same grade as her older brother when school starts in five days. Evan is certain that her presence will cramp his style. Jessie, his sister, finds Evan and tries to get him to play a game with her. He ends up screaming at her: “You ruin everything. You ruined my summer and now you’re going to ruin school I hate you.”(page 9)

The next day Jessie finds a letter from the school in the mail and takes it to their mother to open. It is a note stating that both Evan and Jessie will be in the same class at school. Evan is now convinced that is life is truly over. Understanding how upset this has made her brother, Jessie tries to make things better by offering to help him do the sorts of activities that he likes. Evan refuses to be consoled. Later, she discovers Evan and Scott Spencer constructing a lemonade stand. Jessie offers to help them when she notices that they’ve misspelled lemonade. Thinking that she’s laughing at them, the boys tell her to go away.

In anger, Jessie decides that she’s going to have a lemonade stand of her own. Meanwhile, both Scott and Evan discover many problems involved with running one’s own business, including keeping track of the money, overspending on the product, and the consequences of drinking all of their inventory. The boys quarrel. Not for the first time Evan wishes that he’d taken Jessie up on her offer to help them with the stand as her ability in math could have come in handy.

Later, the boys discover that Jessie has teamed up with Megan Moriarty from Evan’s class to set up their own lemonade stand, and they are doing much better than the boys. Jessie’s plan has been to show her brother that she wasn't a baby and can do a lemonade stand so well that he’ll want to include her, or join her. But, just the opposite occurs. At dinner that night brother and sister have a huge argument in which they both taunt each other and promise to sell more lemonade by the time school starts.

The next day Evan invites three of his friends over and puts a large Keep Out sign on the garage door. When Jessie goes over to meet up with Megan she sees that another girl, Carly, is there. Both of the girls are a year older and they seem to look down their noses at Jessie. Jessie is afraid that the girls are going to be mean to her like some of the girls in her class the past year who had formed the WHJ club (We Hate Jessie).

Evan decides that in order to beat Jessie he needs to make at least fifty dollars. In order to do this he has to find a better location. He ends up going to the town center and setting up the stand there, but after a short while a police officer makes him take everything down and go home because it is illegal to sell lemonade there without a license.

Meanwhile Jessie and Megan are having issues of their own. Jessie knows that having to split the money with Megan, while Evan’s friends have offered to let him keep all of the profits for himself, is going to put her at a huge disadvantage. Doing some math she determines that what they need to do is franchise their lemonade stands. Determined, and with other girls offering to work a franchise stand in each of their neighborhoods, soon Jessie has brought in a lot more money.

Early the next morning, while Evan is in the garage getting his stand ready, Jessie sneaks into his room and counts the money that he’s gathered. She realizes that he is ahead of her. Upset at his earlier words, (that he hated her), she determines to do anything it takes to win. When the boys leave to go make their lemonade stand sign, Jessie sneaks into the garage where they have their lemonade and she dumps flies into the coolers. Then she throws in dirt, just for good measure.

Predictably, when Evan’s customers begin finding bugs in their lemonade and complain, Evan’s mother comes by to see what is going on. They pull the cover off of the cooler and his mother shuts down his operation. On his walk home he begins to put two and two together. He figures out that his sister is responsible for the polluted lemonade. Angered he finds her money box and takes all of her lemonade stand earnings. He doesn't plan to keep it, but plans to give it back after the contest is over.

Evan tries to play a game of basketball with his friends but he is so upset about taking the money that he can’t concentrate. then things go from bad to worse when he realizes that he's lost Jessie's money (which he'd shoved into his shorts before playing ball). Realizing that he’s lost the money that he took from Jessie’s lockbox, Evan is miserable contemplating what her reaction will be. Later that evening, Evan tells Jessie that he’s willing to call it a tie if she is. She is not willing to call it a tie and asks him what his final total is. He tells her that he doesn’t have any money at all.

She opens her lockbox and there’s only a handful of bills there. It is Evan’s money that he’s put in there and ends up confessing to taking the money and losing it. Jessie loses her temper and throws things at Evan, who doesn’t try to deflect them at all. Jessie realizes that he’s not defending himself and stops. Coming together to try and figure out who has taken their money, the two siblings realize that they’ve been acting very badly and that it isn't worth doing if it damages their relationship. Both brother and sister talk openly about why they were so mean to each other. They agree to call it a tie and to work together to try and find a way to get Megan’s share of the stolen money back to her. In the end, both Evan and Jessie have learned that working together is better than working against one another.