Ken Williams (Ken Maynard) is determined to discover the identity of a mysterious killer who preys upon railroads and transportation companies like the ones owned by Jane Corwin (Verna Hillie). Her railroad worker father (Lafe McKee) was the first victim of the murderous fiend known as the Rattler, who is especially difficult to catch because he makes himself appear as other people with a collection of masks, or he effects a strange disguise with eyeglasses, a fake nose, and a crepe-hair mustache. The Rattler — also known as "the Menace of the Mountain" — attempts to control the mountain and its hidden gold from his secret cave filled with strange electronic gadgets.