Cayetana, her boyfriend Paco and Venancio, her foster brother, commit small thefts and, from time to time, spend a few days in jail. Until they meet with Federico, a thief who has traveled abroad and convince them that using European methods success is guaranteed. Paco then decides to act scientifically and seizes a hospital surgical equipment. When they want to realize,  poor Venancio is forced to give an injection to a dentistry patient and, even worse, Paco has to pull out a tooth. And all that, before entering the operating room