Cleo finally finds an upset Carter, who comments on the mixed attitude from Cleo. In the process of looking for Carter, George tells Nikki, who is his crush and Molly's best friend, that this is the best haunted house ever. Cleo then shows Coug that Molly has become invisible. In the annual "Romp the Swamp!" party, Cleo bumps into Coug, who is doubting his relationship with Molly. The group seeks Carter for help to understand the complex data behind the solution. Upon analyzing the duplicated solution, it turns out that Cleo has accidentally made something complex that deals with organic chemistry. Molly scares the security out with a bucket of paint on the floor while Cleo and George sneak in to duplicate the experiment. Cleo tells Molly that the light she refers to earlier is the ability to make everyone around her happy. Molly says that she is also envious at Cleo for being a genius, stating that her popularity would become nothing after high school.
As Molly comes back with the moth in a jar, the sisters take on a trolley heading to school. Cleo later apologizes to Molly, admitting that she admires Molly's light, the power to shine light on everyone around her, and when she can't get it, she would blame Molly for making her feel invisible. After a failed attempt to catch a moth, Molly runs away furiously after a heated argument with Cleo. Cleo and Molly go to the cemetery to catch another moth for duplicating the experiment while George goes to school to set up. Upon observing Molly's cells at home, Cleo and George realize that they have until midnight to find an antidote for the invisibility, or Molly will absorb the sucrose solution completely and become invisible forever. Later in a big lacrosse game, Cleo gets bumped at first, but then slowly gets into the game with Molly's help, resulting in a victory for the team. Things get complicated when George finds out Molly's invisibility, and Coug questions why Molly is constantly avoiding him. To help Cleo get a date from Carter, Molly steals her boyfriend, Coug's, costume, pretends to be Cleo, and asks Carter out. In the process, Molly hears Carter, a boy in Cleo's Science class, talking about Cleo. While Cleo joins the pep circle in the lacrosse team, Molly helps Cleo to get a microscope. Therefore, Cleo has to pretend to be Molly for the day until she can figure out a way to make Molly visible again. She originally wanted to show up in school in her Halloween costume and hope no one would notice, but, unfortunately, her invisibility eventually spread to whatever she is wearing. She cannot miss school that day because in order to play her beloved sport of lacrosse, and be spotted by college Lacrosse coaches, she must attend all of her classes on the first day of the season. Molly wakes up next morning only to be horrified by the fact that she cannot be seen. The moth ends up falling into a cup of Ginger Fizz that Molly is about to drink, and she unknowingly drinks both which renders her invisible the next day. Later that evening, the invisible moth is attracted to the light in the bathroom where Cleo's sister Molly is getting ready for bed. It produces steam that the moth flies through, making the moth invisible, which escapes into the night. As Cleo works separately on the assignment, a moth flies by, and she accidentally spills an unknown chemical into the solution. That night the parents leave, and Cleo's sister is having a party at the house. The teacher makes the assignment worth half her grade, in order to push Cleo to work harder. Perkins (Alex Désert), rejects Cleo's original proposal for a science project and instead gives her a much tougher assignment to determine the composition of a mystery solution, then turn it into transparent crystals. In order to make Cleo challenge herself, her science teacher, Mr. Cleo is an excellent student, but is introverted and somewhat sarcastic and cynical.
Her sister is the most popular girl at school and recognized by everyone, but Cleo is barely noticed by anyone else. Cleo is a teen girl who is always living in the shadow of her popular older sister, Molly.