In Los Angeles in 1870, water was the main concern of everyone there and the most powerful man in town was the Zanjero, or water overseer. And he was often the most corrupt, as well. When Zanjero Bert Rivers turns up dead in the irrigation ditch, or zanja, leading to young widow Maddie Wilcox's vineyards, Maddie has the odd feeling he was murdered.
Then the undertaker's wife, Mrs. Sutton, confirms that Rivers was shot, and not just hit on the head. Maddie finds herself drawn into finding the killer, first to see justice done, and then to save the skin of the one person she knows did not do it - the town's most infamous madam, Regina Medina.
Maddie quickly discovers that Mr. Rivers was not the kind, upstanding civic benefactor he presented himself as, but a most despicable man who preyed on the weak and vulnerable, and cheated everyone else. With nearly everyone having a reason to kill the zanjero, Maddie stumbles on more than a few secrets and finally must reveal her own - that she's a trained medical doctor and not just a woman who is adept at healing for charity.
Even Mr. Rivers' family did not escape his wrath. But just as Maddie begins to suspect them, the youngest son is killed and probably by the same person who killed his father. Spurred on by the need to find the killer before there is another death, Maddie talks to suspect after suspect, only to find that the killer is a lot closer to her than she imagined.