During the mid-1970s, in the Mexican state of Guanajuato, authorities discover a clandestine burial ground. The corpses are from murdered prostitutes. The suspects are three sisters known as "Las Poquianchis".

A guerrilla commando tries to kidnap a politician. In the attempt, several policemen and a guerrillero die. By chance the head of the kidnappers meets an old colleague; to prevent him from betraying them, he kidnaps him.

In Mexico City's infamous Lecumberri prison, three drug-addicted convicts celebrate getting drugs from one of their the mothers. They are found out and locked up in the "apando," the dreaded punishment cell. Protests over the treatment of those held in the cell lead to a bloody confrontation.