Color blindness is the key to a murder frame-up. Hec (Richard Boone) is out to clear some innocent Indians and catch that varmint who killed the three ranchers the Indians are accused of killing. In his scientific way, Hec Ramsey figures out that Indians are being framed for the massacre of a family. He knows Indians wouldn't carelessly leave behind a medicine bag that has been dropped among the victims to throw suspicion on the Indians. Hec's investigation indicates a scheme to scare away settlers.

To save his fiancée from becoming the assassin's third victim, Hec Ramsey must free a prisoner scheduled for execution. However, the influx of strangers in town for the execution complicates Ramsey's search for the killer, leaving him with no other choice.

Appointed Divisional Chief of Police, Hec Ramsey arrives in the city by stagecoach, only to be robbed en route. He reports the incident to his superior, Oliver B. Stamp, upon arrival.