Salvador Medina (Cantinflas) is a country doctor who, finding many different technological advances in the medical field, and the need to adapt to said new technologies, moves to Mexico City to become an intern in the Medical Center of the Mexican Social Security Institute (IMSS).
Salvador immediately clashes with his superior and Head of Training at IMSS, Dr. Miguel Villanueva (Miguel Ángel Álvarez), while growing closer to Nurse Laura (Marta Romero) who, unbeknownst to him at first, is Dr. Villanueva's sister.
In his medical activity at the hospital, Salvador serves various patients by raising their self-esteem and he is jokingly preferred to Dr. Kildare.
Salvador meets Beto (Pepito Velázquez), an eight-year-old patient who has a brain tumor, which has grown enough to disturb his visibility.
Beto's father (Wolf Ruvinski) in particular is opposed to having his son operated, on the grounds that he does not want medical experiments to be done with the child's health, even when surgery is the only way to save him.