The story is set in Versilia in Tuscany, surrounded by the luxuriant nature of the Apuan Alps, and in the bowels of Mount Tambura. Stella and her sister Glenda, along with their two friends Rebecca and Frank who have just arrived from the United States, are involved in a series of incredible events, to the limit of the supernatural. It all starts with a trip in a hot air balloon strongly backed by the boys, despite the concerns shown by their parents. But what started as a unique experience soon turned to tragedy: the four, along with Alfred, the young Turkish driver of the balloon (called "Nautilus"), fall in the middle of a forest because of a turbulence . When they regained consciousness, they are miraculously unharmed, although there is no trace of Alfred. Stella and her friends start looking for a path to get back home, but instead they discover a mysterious underground place. Here begins a journey that will leave the protagonists the sole custodians of secrets that had remained untouched for years, offering to Stella, who is an aspiring writer, a story to tell.