William Riley has served as Sheriff of Lordsburg, New Mexico for sixteen years. In 1902, together with the town's doctor, Brent Ellison, and Mortimer Trask, the local funeral director, they were able to bring justice to the families of six young men who were poisoned with Wolfsbane by Mira Norwood, owner of Ma Baker's Boardinghouse.

Now it is February 1905, and Will Riley is confronted with a more heinous crime: the brutal slaughter of a husband and wife in a raid on their ranch, the perpetrators later identified as members of the Silver Gang. The children of Peter and Suzanne Harrison hid in the stable during the raid then walked to the doctor's home to tell him what happened. Brent Ellison takes them into town to talk to Sheriff Riley.

The evidence is scattered and the case too complex for the Sheriff to investigate without help. He is referred by the Sheriff's Association to the Symington Agency in Santa Fe, and they send a senior detective to Lordsburg to gather and process evidence found on the bodies and in and around the remains of the ranch house. Cynthia Bordeaux has brought her "tool kit" for gathering evidence. A cursory look at the charred remains of Peter Harrison has her perplexed: there are two different caliber bullet wounds in his body. At the ranch, she finds a key on the porch which leads to a post office box, containing a letter written the day after the murders. The handwriting is that of a woman. After reading it, why does Sheriff Riley want to shield the Harrison children from the shocking truth about their father?

The Sheriff and Cynthia return to the ranch to do more digging and are ambushed by the Silver Gang. Cynthia wounds one and kills another, and Will kills the other two, including Ike Hayes, the gang's leader. Bart Irwin, the survivor, has no idea where Frank Bellows, the other gang member, went after the initial raid.

Cynthia leaves for Santa Fe to process and analyze the evidence. Days later, the Sheriff is knifed during an attempted robbery of The Bank of New Mexico. The cut is deep and quickly becomes infected. Cynthia returns to visit Will and takes the bloody knife to the local chemist to determine what contaminated Will's wound. Doctor Ellison then applies an ancient remedy to rid the Sheriff of the infection. As he recovers, William Riley contemplates retirement and he and Cynthia, having fallen in love, make plans to get married.

A freight hauler transporting cow hides from Mexico finds a decomposing body near the border with New Mexico and brings the remains into Lordsburg. Is it Frank Bellows? All will be revealed when Mortimer Trask hands the Sheriff a key piece of evidence, confirming the identity of the corpse.