When a worker is injured during the construction of the Newhouse Tunnel in Colorado, he is taken to the office of Dr. Susan Anderson. There is little Doc Susie can do to help the dying worker, and she is skeptical of the lead engineer’s explanation that the man had been drinking on the job. When the worker’s wife confirms that he wasn’t a drinker, Doc Susie goes on a covert mission to find out what really happened. Deep underground, she begins to suspect that the engineer has been ignoring safety precautions, and she soon finds her own life in peril when the tunnel collapses, leaving her helpless and trapped in the dark with the engineer. Although the engineer promises to put the workers’ safety first if they escape, Doc Susie determines to do everything in her power to prevent more needless deaths, including seeking the help of her friend Bat Masterson, a gunslinger-turned-reporter who can use the power of the press to advocate for change.