Two rival gangs of robbers exist in Mexico city. One band is directed by the gangster Rufino Rufian, whose orders are monitored by his mother. The other band is guided by Kilos, a fat man who does not belong to the same social class as of Rufian. A member of Kilos gang dies in a strange way at home, after going out for dinner with one of Kilos assistants and watching a rats exterminator removes the plague he has at home. The wife of the dead man asks Kilos for a position as a performer in a night club. Later she introduces the mice exterminator to Kilos for a service in the club. A female informer of the rival gang listens to the contract negotiation of the pest specialist and assumes that the exterminator is a cold murderer and reports this information to Rufian.