Professor Sturgess invents a miraculous engine which can draw unlimited power from the atoms of the air. When the professor is killed, his daughter and her fiance must fight to keep the secret of the power engine out of the hands of evil Weston Dore and his henchmen.

Jack Logan is the heir to half of a map to a hidden Indian mine. The trader and villain Jean Gregg sends his chief henchman Mack to make life difficult for Jack. Jack is aided in his quest by the heirs to the other half of the map: Helen Holt and her younger brother Billy, and by a uniformed mystery man known as "The Mystery Trooper".

A young man's father is murdered and the man convicted of the crime escapes prison, leaving a note intimating that seven local men know the real killer's true identity. The murdered man's son sets out to locate the seven men and find his father's slayer.

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.