An au pair girl comes to work for a greedy couple who make money by renting her out to all the other tenants in their building.

Returning from Switzerland to Rome, the boss prof. Salviati, called 'The Prince', finds his business compromised by Rudy, a small local bandit full of presumption, audacity and men ready to kill. Commissioner Baldi a young and brave employee, will fight against them with the help of an ex-employee Rampelli.