Penny, a high school student, secretly acts as a "kindness vigilante," helping people anonymously in honor of her late father, who taught her that small acts of kindness can change lives. After her father passed away in a rescue mission, Penny took on the role of helping others, often retrieving stolen or lost items. One day, she encounters a boy who is also performing secret good deeds, including returning Penny's family's lost photos and letters after their house fire. This boy, Adam, reveals that he's been in love with Penny since seventh grade and has been inspired by her kindness.

Penny, determined to find out more about Adam, sets a trap using a ring from her best friend, Ella, hoping Adam will retrieve it and reveal himself. However, her plan goes awry when Adam is arrested while trying to retrieve the ring. During his court case, many people whom Adam had helped come forward, testifying about his good deeds. The judge acknowledges the positive impact of their actions but still sentences both Adam and Penny to two years of community service for their illegal activities.

Despite the setback, Penny and Adam decide to continue their mission of spreading kindness, but this time legally. They plan to start a kindness club at school, allowing them to help even more people with the support of others, turning their vigilante efforts into a positive, organized movement.