A serial killer is on the prowl for the seven members of a professional posse, the Trackers, that served north Texas in the early 1890s. Six of the posse have been murdered…only one is left. MASON FLYNN Will he be assassinated? Can time travelers, Bone and Loraine, catch the sniper? Sherlock Holmes said: "…when you have eliminated the impossible, whatever remains, however improbable, must be the truth?"