Laos, 1866. Hirondelle d’Or, a mysterious spy, follows closely the Mekong exploration mission led by Captain De Castel. As the expedition moves deeper into the country, the young woman and the military man attract each other, become closer and fall in love. The botanist Odile Dubuisson and her daughter Marie explore the jungles of northern Laos, 150 years later, following in the footsteps of their illustrious ancestor. Referring to a poem by the explorer: On the branch of the bamboo / The larva of the butterfly / One day will become a flower, Odile understands that he has seen the giant bamboo bloom. She also understands that the giant bamboo will bloom again. This is the perfect opportunity for her to witness a rare event. From then on, the story intertwines present and past.