The President of México sends Rosaura Salazar (María Félix), a young teacher, to educate a remote rural village known as Río Escondido.

While walking there in the heat, Rosaura collapses and is saved by Felipe (Fernando Fernández), a student doctor on his way to a nearby town for his social service.

At Río Escondido, the tyrannical local boss don Regino Sandoval (Carlos López Moctezuma) initially blocks her plans to reopen the school.

After becoming ill himself, don Regino calls for Felipe, who agrees to cure him in exchange for vaccinating the townspeople and letting Rosaura open the school.

In revenge, don Regino breaks into the school at night and attempts to rape Rosaura, but she kills him with a gun that Felipe secretly gave her for protection.