By the Sun's Rays: Frank Lawler, a clerk for a mining company, colludes with a bandit gang about the timing of gold shipments with a mirror signal system and has designs on Doris Davis, the daughter of the local branch manager. The company's main office dispatches their top detective John Murdock, who goes undercover to expose the scheme and rescue the Doris from the unwanted advances of the dastardly Lawler.