One personal tragedy after another has struck Alexandra Morse, a rising star in the FBI who specializes in hostage negotiation: her father's shooting death in a robbery, her mother's diagnosis of advanced ovarian cancer, and a misstep on the job that left her face scarred and a fellow agent dead. Now Alex's sister, Grace, lies dying in a Jackson, Miss., hospital after suffering a stroke. Alex arrives from Washington just in time to hear Grace say that her husband has murdered her. After Grace's death, Alex learns that Dr. Eldon Tarver, a brilliant scientist in need of funds for research into developing a biological superweapon, has teamed with a Mississippi divorce attorney who offers select clients the opportunity to avoid a protracted court fight by arranging for their spouses to die. When Alex identifies the next intended victim, Dr. Chris Shepard, she goes undercover as one of the idealistic doctor's patients and soon finds herself in a race against Tarver as well as her own superiors, who have not sanctioned her investigation.