The murder Kinsey Millhone is asked to solve is eight years old, and Kinsey is doubtful that there is anything further to add to the case, but agrees to look into it as it is unlikely for a recently released prisoner on parole would ask to have things stirred up if she were really the guilty party. Nikki Fife claims to be innocent of the crime and says she waited until she was released from prison so that she could find someone who would really help her to find the true killer of her husband. Kinsey is not entirely sure she wants the case, but agrees to look into it a little bit to see if there is anything that did not come out at the trial. After visiting her old friend, Con Dolan, at the police station where she is able to review the case files, Kinsey discovers that there was something more after all to the case. Not only was Laurence Fife killed with powdered oleander, but a young twenty-four-year-old accountant in West Los Angeles died four days later of the same poison. The coincidence is too much to miss, but rather than appearing to clear Nikki of her husband's murder, Detective Dolan believes that Nikki is guilty of not one but two murders.

Kinsey decides to take the case because she truly believes that Nikki is not guilty and that there is a murderer who got away with murder not once, but twice. As she delves into the files and lives of the people involved, Kinsey is met with deceit, deception, misdirection, and hostility. One thing about Kinsey is that when she feels that there is a miscarriage of justice going on she will work night and day to correct it. Her understanding of Nikki Fife's case changes almost on a daily basis and the old facts that she brings to light are making someone nervous. Within a short time of taking the case and interviewing possible suspects or witnesses, one woman, Sharon Napier, is shot to death in her apartment. Kinsey sleeps through her appointment with Sharon and feels somehow responsible for her death, as if she had led the murderer to Sharon.

Following leads that take her from Santa Teresa to Las Vegas to Los Angeles to Salton Sea, Kinsey is determined to discover who the murderer is. Because of the similarities in the two poisoning deaths, the police and Kinsey originally believe that there is only one murderer, but as more and more details about the case come to light, Kinsey realizes that there is very likely more than one person who has committed murder, and neither one of them has yet been caught. Nikki Fife is truly innocent of the murder of her husband.

Kinsey is very involved in the case, and as a result becomes involved with the people linked to the case. She becomes very close to her client, Nikki, and Nikki's deaf son. She starts a physical relationship with a potential suspect, Charlie Scorsoni, and is uneasy about it, feeling that getting romantically involved with a possible suspect is simply bad business. It turns out that her intuition is correct. Laurence Fife's first wife, Gwen, is the one who poisoned Laurence. However, when Gwen is killed the day after Kinsey confronts her about the murder of her former husband, Kinsey realizes that there really is a second murderer and the only one left is Charlie Scorsoni, an estate attorney who has found it easier to skim off the funds of his deceased clients than to make all of his money honestly. When Laurence was killed with oleander, Charlie determines that in order to get the young, tenacious, and increasingly suspicious accountant out of the picture, he would have to carry out a copy-cat murder of Libby Glass and hope that both murders get pinned on the same suspect.

Unfortunately for Charlie, Kinsey unravels the entire story, delving deeply into the lives of people she has never met before, to come to the truth of the whole event. Once she determines that Charlie is guilty, she has to find proof, which she finds at John Powers's home. John is Charlie's law partner. Charlie has used John's black Lincoln to run down and murder Gwen Fife. Kinsey finds damage on the Lincoln that is consistent with a hit and run accident. The chase is on at this point, when Charlie shows up and chases Kinsey into the ocean, onto a beach, and finally into a dumpster where Kinsey must turn on her former lover and shoot him to death.