In the imaginary town of Petrasicca, Sicily, two cousins, Franco and Ciccio Scontentezza, who have always been rivals due to personal differences, receive a lucrative assignment: to offer their land and their availability to grow some mysterious plants.
The entrepreneur commissioning the operation is a certain Pierre, a shady drug dealer who intends to exploit their naivety and ignorance to grow marijuana plants for illegal purposes. Pierre orders the two cousins to notify him by telegram when the plants are ready for harvesting.
The two cousins, inexperienced and believing in Pierre's good faith, follow the instructions and see the plants grow, mistakenly believing them to be a variety of salad vegetable similar to rocket.
Franco and Ciccio, attracted by the prospect of a profit from the sale, start stealing the plants from each other at night, until they destroy them all. The popularity of the plants is due to the previous theft of some of them by an acquaintance of the two, who had experienced their hallucinogenic effects, causing an uncontrolled increase in sexual desire.
The news spread quickly among the villagers, attracting the attention of the local carabinieri marshal and a narcotics investigator named Joe Ragusa. The marshal explains to Ragusa that the two cousins are naive, as they believe that 'Maria Giovanna' is the name of a woman, not the hallucinogenic plant.
After a fruitless interrogation, Joe Ragusa decides to let Franco and Ciccio go free so that he can follow them to discover the identity of the drug dealer.
Franco and Ciccio, without the required goods, go to Rome in search of Pierre, buying mixed vegetables to present themselves with something in their hands. Pierre, angered by their presence, nevertheless decides to pay the two cousins. But when he discovers the contents of the 'merchandise', he feels mocked and begins to seek them out for revenge.
Franco and Ciccio, unable to understand the gravity of the situation, flee and end up in Spain, pursued by Pierre and his men. Thanks to the luck that has always accompanied them, they manage to escape an enraged bull and have Pierre arrested thanks to the cunning of Joe Ragusa, who had always watched them in the shadows.
Back in Petrasicca, their rivalry is rekindled, but they are suddenly drawn in by a girl named Maria Giovanna. Hearing the name, the two cousins flee in terror, convinced that she was the cause of all their problems.