It's St. John's eve, and voodoo drums sound throughout New Orleans. Yancy, Pahoo, and a skeptical John are swept up in a web of intrigue when a visiting foundry owner is struck down by a voodoo curse while visiting his fiancee.

While checking his silver mine in Virginia City, Yancy discovers that a crook has faked Yancy's death and is holding the granddaughter of Yancy's partner hostage to force her grandfather to hand over the mine to the "Widow Derringer".