Susan, an American researcher, is writing an article for an important scientific journal on the history of the American biologist and physiologist Ancel Keys. Since Keys lived in Cilento for his studies, Susan carries out her research in Campania where she has to interview the Italian nutritionist Vanni Proietti, who will provide her with valuable material for her article. The two meet in a restaurant where a casting of young aspiring you-tubers is taking place. Among them, there is Ciro, an overweight child, accompanied by his uncle Sasà. And the eating habits of the two are the exact opposite of what Keys preached.

Little Tobia lives with his grandfather Remo, who always tells him fascinating stories. His favorite one tells that at the end of the rainbow you can find a crown of colored diamonds, from which the seven beams of light that form the splendid arch are generated. Tobias manages to convince his grandfather to face the journey to the mountain where he is sure he saw a rainbow spring forth. Tobias, together with his friends Luke, Mack and Ava, the dog Fluffy and the cat Kitty, will set off on a great adventure immersed in nature ruined by man's carelessness.