Rabies kills. Can it also cure? Tessa Price, PhD, knows what it’s like to lose a child to a genetic disease. To spare another mother this pain, she invents a radical new gene therapy that might save the life of seven-year-old Gunnar Sigrunsson. Unable to get regulatory approval to treat Gunnar in the US, she takes her clinical trial to the Palacio Centro Medico, a resort-like hospital on a Mexican peninsula where rich medical tourists get experimental treatments that aren’t available anywhere else. When the hospital is taken over by a brutal drug cartel, Tessa hides with a remarkable trio of Palacio clients—rich Texan Lyle Simmons, his much-younger Brazilian girlfriend, and his protection dog, a German shepherd named Dixie, only to learn that the gangsters aren’t the only deadly threat they face. A rabies-like infection that began in the Palacio’s research chimpanzees has spread to humans. Tessa investigates and finds a shocking connection to her gene therapy experiment. In the wake of this discovery, Tessa must weigh the value of one human life against another—including her own.