A forensic neuropsychologist at Boston's prestigious Pearce Psychiatric Center and an expert defense witness, Peter Zak regularly testifies at murder trials on issues like a defendent's conception of right and wrong or the reliability of a witness's memory. This time a lawyer calls Peter to the scene of a crime - his client Nick Babikian has just found his wife brutally stabbed and floating in their backyard pool. The lawyer wants Peter to assess Nick's state of mind. A brilliant but paranoid man who's made millions inventing and marketing his own computer role-playing game, he was working in the house while his wife was stabbed, and he's certain to be accused of wielding the knife.

Nick claims his innocence, but he has no proof, though certainly some of what he claims seems true. For example, there are signs his wife was having an affair. And oddly, the longer they work together, the more Peter relates to Nick's feelings. For Peter himself becomes more and more convinced that his own wife's killer, a man who's supposed to be serving life in prison, is somehow tormenting him at home and at work.