Thelma, Alma, Suzanne, and Roméo – four close-knit yet very different cousins – overhear their parents talking about a treasure that’s hidden in the forest around their vacation house. They immediately hatch a plan to set off in search of it! Their journey is full of tiny, wondrous discoveries. When they reach the pond, they notice some frogs slipping underground. Without thinking twice, the children follow them and discover a cave where a ceiling lit by fireflies glimmers like a starry sky.