The four friends Hannah, Sarah, Sofia, and Lisa can hardly wait for school to finally be over today. The weekend is just around the corner, and they want to spend it together at the horse farm in Lakeside, which belongs to Hannah's parents. Plus, it's Hannah's birthday! When the four girls set up their sleeping area in the barn that evening, they accidentally discover an old chest with the initials H and C. Inside the chest are many old photos, a completely yellowed flag, and an old map of the area with markings. The girls set out the next day to uncover the secrets of the map, make an astonishing discovery, and decide to form the Horse Club!.