After Mary Henderson's father is killed during a stagecoach robbery, she suspects that a mysterious stranger known as "The Spider," who recently saved her younger brother from a cattle stampede, is head of the gang responsible. He and two other men are arrested, but quickly break out of jail. They split up, then Mary, who has found the money stolen in the robbery, is kidnapped by the two other men. After The Spider rescues her, and the two men are apprehended, it is revealed that The Spider is a Marshall who has been working undercover to capture the outlaws.
—AFI