Dr. John Meredith has been driven from civilization by the criminal activities of his twin brother Bradley Meredith. With his infant daughter, he settles in the African jungle, where his ability to cure the native ills has resulted in his virtual control of the Masamba tribes, who possess vast diamond mines coveted by a gang of crooks. They use Shamba, a witch doctor jealous of Dr. Meredith's influence over the tribe, to further their schemes. They lure Dr. Meredith away from the jungle, and he is murdered by "Slick" Latimer. The natives believe that a sacred amulet is the secret of Dr. Meredith's power, and Shamba attempts to kill Nyoka, Meredith's now-grown-up daughter, to obtain the amulet (which actually contains the secret to the entrance of the Caves of Nakros). Jack Stanton rescues her and assists her in her efforts to recover the amulet. Latimer works with Shamba, and with Bradley Meredith, who poses as his murdered-brother so successfully that even Nyoka does not realize the deception.

American, British and Chinese secret agents battle the Japanese Black Dragon Society, a secretive ring that smuggles enemy agents into the U.S. disguised as mummies.

A sea captain about to be hanged for a murder he didn't commit is rescued from the gallows by two of his crewmen. They head for the island of Pulinan, where they believe the real murderer--the captain's former partner--is hiding so the captain can clear his name. As it turns out, their troubles are only beginning.

Crime lord Jim Belmont escapes FBI custody and begins a reign of thievery that is thwarted at every turn by Jerry Blake, the FBI's Operator 99.

Girl looking for father who disappeared years before in a jungle, finds herself battling greedy civilized people and savages alike.

Western settlers are being driven off their homesteads and ranches by a combination of Indian raids and attacks by bands of mysterious outlaws. The government sends out famed Indian scout Kit Carson and army officer David Brent to investigate, and Carson discovers that a villain named Pegleg controls an outlaw gang called the Black Raiders, and is using them and the Indians to drive out the settlers so he can establish his own empire. He determines to set a trap to expose the identity of Pegleg while avoiding traps and ambushes that Pegleg is setting for him.

Three government aviators called the "Flying G-Men", one of whom is disguised as "The Black Falcon", fight to protect the US and its allies from an enemy spy ring and to avenge the death of the fourth Flying G-Man.

An expedition arrives on an uncharted jungle island to rescue the local natives, led by a jungle boy, from a volcano that is about to erupt.

A famous detective sets out to discover who stole $2 million in bonds.

A young radio cop and a beautiful girl try to stop an international criminal gang from getting their hands on the formula for a new bulletproof steel.

Ken Williams is determined to discover the identity of the mysterious Rattler, who preys upon railroads and transportation companies like that owned by Jane Corwin. The Rattler is especially difficult to catch because of his skill at disguising himself as other people.