"The Secret of Ka-Zar's Origin!" by Lee and Kirby/Romita. 20 pages.
Daredevil has lost his radar senses in the battle between Plunder's troops and the Swamp Men. Ka-Zar has left to go search for healing herbs, and now Daredevil is helpless as the Ape Man Maa-Gor happens upon his resting place. Lord Plunder saves Daredevil from the clutches of Maa-Gor, and when Ka-Zar returns with the medicine, Plunder tells Ka-Zar that he is his brother. Each own half of a medallion given to them by their father before his death. Their father had discovered a new substance that would vibrate and disintegrate metal (later dubbed Vibranium), and locked it away in a vault, the two halves of the medallion serving as the key. Plunder betrays Ka-Zar's trust, capturing him, but not before Ka-Zar gives the medicine to Daredevil, returning his powers. Plunder takes Daredevil and Ka-Zar back to his father's castle, where he hopes to open his fathers vault, but Daredevil helps the two to escape. Plunder's butler Feepers is working to get the Vibranium himself, and has an agent on Daredevil and Ka-Zar's trail.
Reprinted in Ka-Zar (1970) #2.