The People of the Black Circle by Robert E. Howard

The death of Bunda Chand, King of Vendhya, via a curse channeled to his soul through a lock of his hair leads to the ascension of his sister, Devi Yasmina, who vows to get revenge on his killers, the Black Seers of Yimsha. Conan, meanwhile, has become chief of a tribe of Afghuli hillmen. Seven of his men have been captured by the Vendhyans and Yasmina intends to use them as collateral to force Conan to kill the Seers. However, Conan infiltrates the border fort where they are held and kidnaps the Devi instead (with the intent of exchanging her for the seven men). The problems are complicated by Kerim Shah, an agent of King Yezdigerd of Turan, who arranged Bunda Chands death in order to lead an army through the mountains and invade in the subsequent confusion and turmoil. His contact with the Black Seers, Khemsa, has fallen in love with the Devis maid Gitara. They decide to strike out on their own, kill the seven hillmen and pursue Conan and Yasmina to kill them both as well...