The character known as Manco is a bounty hunter, who crosses paths with a former army officer, Colonel Douglas Mortimer, as they both uncover the escape of a notorious bank robber named "El Indio." His gang has brutally murdered all but one of his jailers during the breakout. While Indio is on a violent spree, brutally killing the family of the man who once captured him, we learn about his eerie psychological burden—a musical pocket watch he carries, taken from a woman he brutally assaulted and murdered. This haunting memory drives Indio to self-medicate with a powerful drug to escape his past.
Planning a grand heist at the Bank of El Paso, rumored to hold nearly a million dollars, Indio orchestrates his plan with his gang. When Manco arrives in town, he quickly notices Mortimer, who had arrived before him, engaging in a provocative exchange with a hunchback named Wild who is scouting the bank. After a tense standoff, the two men establish their mutual intentions and agree to team up. Mortimer convinces Manco to infiltrate Indio's gang by helping free one of Indio's friends from jail, despite the robber's initial suspicions.
Indio then tasks Manco and three other gang members with robbing a nearby bank in Santa Cruz. However, in a twist of fate, Manco ends up gunning down his companions and sends a false telegram to alert the sheriff in El Paso. While the gang attempts to break into the El Paso bank, they leave empty-handed when they fail to open the safe. After returning, Manco manages to maintain Indio's trust by fabricating an injury thanks to Mortimer's assistance.
The gang relocates to Agua Caliente, where Mortimer is laid in wait, leading to a showdown that results in Wild's demise. Indio entrusts Mortimer with the safe, believing in his expertise to open it without demolishing it. Following a night of deceit, Manco and Mortimer manage to hide the loot, but they find themselves captured and beaten shortly thereafter. Indio cleverly orchestrates a plan to eliminate the two bounty hunters, but a twist emerges when Groggy realizes this betrayal, leading to a deadly confrontation.
In a climactic sequence, Mortimer confronts Indio and reveals his true identity, leading to a final showdown where he challenges Indio using the eerie melody of the pocket watch. As tension mounts, Manco passes his gun to Mortimer, declaring, "Now we start." The final shot delivers a dramatic conclusion as Mortimer shoots Indio down.
Retrieving the watch from Indio's lifeless hand, Mortimer reflects on his family ties to the woman from the watch's vignette, and having claimed his revenge, he walks away from the bounty. Manco, on the other hand, gathers Indio’s body as well as the others, finally claiming the hidden treasure for himself as he rides off into the sunset, leaving behind a haunting legacy of betrayal and vengeance.
