This is a Kate Jepp Mystery.

Wealthy cattle baron Charles Kingsley is fatally shot in his home, a flat granite stone placed beneath his head. On the wall above his body among Western memorabilia, Kate Jepp notices an original invitation to Tom Horn's hanging. This notorious gunslinger, who tracked and shot cattle rustlers in the late 1800's, also left behind a stone as a symbol of vengeance.Alerted by this link to Wyoming's bloody past, Kate looks for would-be seekers of revenge. Kingsley's new bride has displaced his niece, Mary Ellen, as his heir, and he has been engaged in a fierce battle with Sam Swen, whose foreman, Ty Garrison, may be a modern-day hired gun. Each step Kate takes places her in the path of deadly vengeance.