Hal Keen sets out to get to the bottom of a mystery that threatens the safety of a whole community.
THE MYSTERIOUS ARAB
Mystery, excitement, murder in a scientist's camp in the jungles of Africa, where hate, revenge, and suspicion lead to tragedy.
THE HERMIT OF GORDON'S CREEK
The disappearance of two airmail pilots leads to a mystery that centers about an abandoned mine and a strange old man.
KIDNAPPED IN THE JUNGLE
A hint of buried treasure in the ruins of an old French mission leads Hal deep into the Central American jungle.
THE COPPERHEAD TRAIL MYSTERY
Baffling and blood-curdling events center about the ranch where Hal Keen and his friends had gone in search of gold.
THE LONESOME SWAMP MYSTERY