Olmo, eighty years old, looks out of the window of a building in the suburban area of a city. His eight-year-old grandson Giulio is reading him an article from the newspaper about melting glaciers, the greenhouse effect, methane and CO2... “What is C-O-2?” asks the child. “Do you remember the carbon dioxide we studied?” says Grandpa. “The one the trees breathe?” asks Giulio. The day after, they’re leaving for a short tour instead of going to school, searching for an old tree.