Son of the White Wolf by Robert E. Howard

WHEN FRAULEIN OLGA VON BRUCKMANN, known as a famous German secret agent, arrived at the tiny Arab hill-village of El Awad, it was in a drizzling rain, that made the dusk a blinding curtain over the muddy town.

With her companion, an Arab named Ahmed, she rode into the muddy street, and the villagers crept from their hovels to stare in awe at the first white woman most of them had ever seen.