The Light of Western Stars by Zane Grey

Madeline bolted the door, and, flying into the kitchen, she told the scared servants to shut themselves in. Then she ran to her own rooms. It was only a matter of a few moments for her to close and bar the heavy shutters, yet even as she was fastening the last one in the room she used as an office a clattering roar of hoofs seemed to swell up to the front of the house. She caught a glimpse of wild, shaggy horses and ragged, dusty men. She had never seen any vaqueros that resembled these horsemen. Vaqueros had grace and style; they were fond of lace and glitter and fringe; they dressed their horses in silvered trappings. But the riders now trampling into the driveway were uncouth, lean, savage. They were guerrillas, a band of the raiders who had been harassing the border since the beginning of the revolution. A second glimpse assured Madeline that they were not all Mexicans.

The presence of outlaws in that band brought home to Madeline her real danger. She remembered what Stillwell had told her about recent outlaw raids along the Rio Grande. These flying bands, operating under the excitement of the revolution, appeared here and there, everywhere, in remote places, and were gone as quickly as they came. Mostly they wanted money and arms, but they would steal anything, and unprotected women had suffered at their hands.