Geologist Em Hansen is out of work, and her bills are pilling up. She is also recovering from the death of her father. She jumps at the offer of a job doing some detective work for California Senator George Pinchon. His daughter, Janet, was found dead in a drainage ditch on a Californiat ranch, and he wants Em to find out what happened to her because the police do not seem to be doing very much about the case.
Janet was an environmental geologist working for a firm which was investigating contamination from buried gasoline storage tanks. Em applies for and gets Janet's job with the company, and soon comes to believe that there is something suspicious in their operations. Em finds that she and Janet have more in common than just being geologists. Em fits in Janet's clothes, and even looks a little like her. Em's investigation uncovers shady land deals by the local citizens, and a very secretive family named Karsh who own the ranch where Janet's body was found. Their adult son, Matthew, is mentally retarded, and Em find him to be very threatening even though the neighbors say that he is very nice.
Em is attacked quite viciously by the person whom she believes killed Janet. Em doesn't know whether the attack occurs because she is close to the truth about the murderer or because of her resemblence to Janet, but she does realize that she must prove who the murderer is in order to save her own life.