When outlaws in the Nueces Strip ruthlessly massacre innocents by the light of every full moon, Texas Ranger C. W. Wallace is dispatched to stop the next bloody murder. The crime and brutality rampant in the 1877 South Texas brush country threatens people in every community, but using Texas Rangers to combat the problem is as controversial as the violence itself, so C. W. rides alone and is rarely welcomed where he goes. To track the cattle thieves, he and other Rangers need the civilian population to become their extra eyes and ears. Clues at an isolated homestead suggest that a secretive young widow could be a valuable resource, but C. W. is hesitant to trust her. In an effort to identify the ringleaders, C. W. and the widow, Esther, ride breakneck for the border and illegally cross the Rio Grande into Mexico. But disaster plagues them, and C. W. realizes Esther is herself a target for death, even as his affections turn toward her. Now Ranger Wallace must do all he can to prevent Esther's murder and discover where the marauders have planned the next moonlight massacre.