The Hour of the Dragon is also known as Conan the Conqueror. It was first published as a five part serial in 1935-36.
The Necromancer, Xaltotun, is resurrected after three thousand years, to aid in a plot to overthrow the rule of King Conan in Aquilonia. The arts of Xaltotun paralyze Conan on the eve of battle, the battle is lost and Conan taken alive. Freed by a dancing girl Conan escapes through the black pits and learns that only the cosmic jewel "The Heart of Ahriman" can defeat the sorceries of Xaltotun.