There is in France, somewhere in the heart of the Alps, an extraordinary river, a jewel where you can find the largest brown trout in the world … No need to run therefore the rio of South America, the rivers of Mongolia or the mythical Socca from Slovenia. Like a long and jealously guarded secret, this pearl located in Haute Savoie has survived the centuries without ever being advertised. Seeing the size and weight of the catches made here, we can understand this wise silence of local fishermen. But which river is it? What are these giant trout? Who catches them, and how? So many questions to which this documentary film will answer, mixing unusual fishing scenes, scientific investigation, and ecological bias …