The story involves a montonera that, lacking arms and men, decides to use a novel strategy for taking down a royalist fort. There's a pretty strong description of the desperate situation they are in at the beginning of the story. They manage to eke out an existence, relying on some of the local flora and fauna for nourishment, but it is not a particularly hospitable environment. This is an instance where Lugones' fondness for description is quite effective, both giving a nice sense of place to Salta and adding to the impression of hardship.
There's also and interesting section in the middle which gets into the gaucho attitude to the horse, which is an integral part of the culture. While reading Don Segundo Sombra, I was struck with how the gauchos seemed to have a word for every different kind of horse, even down to the different types of coloring.
The men finally decide to use the stampede the horses at the fort (shades of "The Horses of Abdera"), causing destruction, a decision they are not entirely please with. The description of the stampede, staged as it is at night, is quite striking.