In the years after the American Civil War, the West is wild, and the East is run by the robber barons battling each other for power and money. The range is untamed and blood-soaked, and the cities are dazzling tributes to culture and questionable scientific development. Outlaws roam free on the frontiers, and crooked lawmen and Pinkertons compete with lawless bounty hunters for the prices on their heads. Tess Mercury and her posse are the best damn bounty hunters in the West. When Tess and her posse, trick shooter "Bonny" Quimby Burton, mad scientist "Lightning" Hazel Harley and Vaughn, a former slave, are run out of town after brawling with some card players who don't take kindly to being swindled by Quimby, Tess decides a life of leisure just doesn't suit them.

They go in search of a new bounty to hunt and discover the case of Zeke "Angel" Cooper, a Pinkerton wanted for murder in Boston. The hunt for Angel leads them through the untamed frontier where Indians lie in wait, young men fighting for honor are shot dead in the streets, Che Chucho and his posse of peculiar bounty hunters are hunting them, and savvy, sophisticated Madam Esther Star courts the big bugs from D.C. at her famous brothel, the Governor's Mansion. When Tess and her posse finally run into Angel, they're tangled up in an even greater mystery involving faulty death rays, crooked lawmen, missing secretaries, murdered government agents, bribery, corrupt Congressman, clockwork horses, Tess' long lost husband, and Sterling Rush, the technology robber baron who might just be a more dangerous enemy than any of them have ever encountered.