Dr. Daniel Rinaldi, a Pittsburgh psychologist, gets involved in two police cases. The first involves Wesley Currim, an unpleasant, wise-cracking young man who's confessed to the murder and decapitation of rich executive Edward Meacham. Wes's mother Maggie, however, swears she was with her son at the time of the murder and implores Dr. Rinaldi to help the boy.
At the same time Rinaldi is working with the FBI on a case involving serial killer John Jessup, who was convicted of murdering four prostitutes. Jessup, who was killed in a prison riot, had an admirer who wrote him complimentary, supportive letters signed 'Your Biggest Fan.' The admirer is now on a murder spree of his own, killing people responsible for Jessup's imprisonment and death. This seems to includes a prison guard, the judge, the prosecutor, jurors, the defense attorney, and Lyle Barnes, the FBI profiler who fingered Jessup. Barnes now suffers from night terrors and needs the help of a psychologist.
Local police are working with the FBI to protect potential victims and nab Jessup's admirer. They're hampered, however, because the killer seems to have inside information: he knows where the authorities are hiding potential victims, knows when they're about to question a witness, etc. Clearly, the investigation is compromised in some fashion.
While working on the cases Rinaldi can't seem to go a day without getting involved in a life-threatening situation such as chasing down a gunman, being run off the road by truck, putting himself in the path of a murderer, and so on. This seems unwise since Rinaldi apparently doesn't carry a weapon or possess martial arts skills. To me, he's somewhat of an unrealistic character - a sort of psychololgist/superhero - but he seems to be a decent enough guy. There's also a touch of romance in the story since Rinaldi gets together with Detective Eleanor Lowrey, a woman he's been attracted to for some time.
Eventually Rinaldi comes across information that's pivotal to both cases which leads to the book's climax. I thought this was a pretty good story with interesting characters and a nicely-constructed plot.