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A high school girl from Ukraine and her French cousin, travelling through the Pyrenees, come across a natural wonder - the underground river Fontestorb, whose flow stops every half hour. Later it turns out that it hides other secrets. The two teenagers try to solve them and suddenly find themselves outside the Time Gate, right in the middle of the Albigensian Wars in the south of France. In medieval Languedoc, they have to go through many dangerous adventures. They risk their lives to save their new friends from the Inquisition and discover an incredible family secret...