An early summer afternoon in the 1990s. While their parents are taking a nap, sisters Lotti and Malibù (using the nicknames they have given each other) sneak off in secret to go to a bar, hoping to meet the boy they both fancy. Their youngest sister Puca insists on going with them, threatening to wake their parents with her screams if they leave her behind. The three sisters set off together, and as they pass the beach, Puca walks closer to the water’s edge and swears she has seen a mermaid. At the bar, Lotti and Malibù are swept away by their teenage drama and end up losing sight of Puca. Thus begins a search that will bring the two sisters toward a final confrontation, followed by a glimpse of the mermaid disappearing into the water. With that image, they realise their childhood is gone forever. Then, the unexpected happens when they return home to tell their parents…