With the help of green filter created by Professor Erasmus, Italian cities transformed into green gardens. Suddenly, however, the plants are affected by a strange disease. Professor Erasmus with the help of two children, Michele and Lorenza, discovers that the illness is due to the actions of two malicious scientists polluting the atmosphere. Through acid rain the infection is transferred to the plants that get sick. The Professor returns to Milan to solve the problem. In his effort, Chlorophyll, an alien little girl, will help.