Hank and Johnny are assigned to investigate a series of raids against Mexican towns along the border. They come to suspect that German troops who are disguising themselves as American soldiers are committing these attacks in order to instigate a war between the US and Mexico.
Johnny and Hank come into a town that is having problems with its oil wells being sabotaged, and the residents are blaming Indians from a nearby village for the damage. The two try to find out who's behind the sabotage before the angry townspeople attack the village and start an Indian war.
A prison in Texas is taken over by a German military intelligence officer, who believes that the inmates would provide a fertile ground for recruiting saboteurs. Hank and Johnny have to come up with a plan to break into the prison and stop the German.