Winston Garano, an investigator with the Massachusetts State Police was sent to Knoxville, Tennessee to attend the National Forensic Academy by his District Attorney, Monique Lamont. She summons him back Cambridge at short notice and the pair meet at the faculty club. Lamont wants her police force to be responsible for solving old crimes using the new forensic techniques Winston has acquired (a campaign which she is calling "At Risk"). She has the reluctant support of Governor Crawley who believes this may attract voters.
At their meeting at the faculty club, Lamont explains to Win that she has found a case for him to solve using his new DNA knowledge. It involves the brutal murder, and possible attempted rape, of an elderly lady (Vivian Findley) in Knoxville twenty years that has never been solved. Winston is not convinced, but Lamont thinks this case will garner gratitude from the people of Tennessee if it succeeds, and is far enough from Massachusetts to be brushed under the carpet if it isn't successful.
Winston goes to visit his grandmother. Throughout their conversation she reads Tarot cards for Winston which seem to suggest he should be cautious of Monique. Winston receives a phonecall from a mysterious person who tells him to meet him at a cafe at midnight. Win is suspicious, but leaves his grandmother's, almost running over a dog in the process. He recognises Miss Dog as belonging to a slovenly neighbour and drives her back home. On seeing how afraid she is of her owners, Win tries to buy the dog, but doesn't have enough money to convince them to sell her.
As instructed by the mysterious caller, Win goes to the Rosebud Diner. He waits until after midnight but no one shows up. As he is leaving the waitress hands him a note which someone left for him two hours earlier. Win reads the note in his car. It is a threat saying "You're the one AT RISK, half-breed". Win calls Lamont who sounds strange. He then calls Sykes, a fellow investigator at the National Forensic Academy. He asks her to track down the original police file for the Knoxville murder case Lamont wanted him to solve. Win then decides to drive to Lamont's home, partly because he wants to quit the case, and partly because he feels that something isn't right. He enters by her open back door and finds Lamont upstairs, naked and tied to her bed, and being held at gun point by a Hispanic assailent. Win tackles the criminal, seriously injuring him and unties Lamont.
Lamont is taken to hospital where she reveals that she was held at gun point on entering her house, and then tied up and raped. She is examined for medical evidence. Her assailent is identified as Roger Baptista, but he dies of the injuries he sustained when attacked by Winston. Win reveals that he found a can of gasoline and rags in Lamont's back garden. Lamont realises that Roger had planned to murder her and then burn her house to hide the evidence. Sammy tells Winston that Lamont has already allowed a press release about their re-opening of the Vivian Findley case to go out, and that Roger had £1,000 of new bills in his back pocket, suggesting he was paid to kill Lamont. Lamont wants Winston to act as her personal protection and to prioritise finding out who is responsible for ordering her assassination as she is concerned that her bid for governor may be compromised. Winston is unwilling to help her and wants to take a couple of days off. Meanwhile, Sykes searches through the basement of Jimmy Barber, the deceased detective who worked on the Vivian Findley murder case, looking for the original police file.
Lamont half-threatens Winston, by suggesting she might make his attack of Roger seem uncalled for in her testimony if he doesn't assist her. Winston agrees to help her. To avoid the press, Lamont is flown by helicopter from the hospital to Boston, where she reveals she has an apartment. She is met by Sergeant Small, who will escort her there. Sykes finds some telephone bills in Jimmy Barber's basement. On checking them she finds it suspicious that Jimmy made seven long distance phone calls on his home phone on the evening of Vivian Findley's death.
Winston returns to his apartment where he receives a call from Sykes. She tells him that she has only found one document with the correct case number, and it is a list and pictures of Vivian Findlay's blood stained clothes from the night when she was murdered. Sykes and Winston realise something unusual is going on as the clothes are size 10 tennis gear, and it would not be likely that the elderly and diminutive Vivian Findlay would have been wearing them. Sammy knocks at Winston's door to inform him that Lamont wants him.
Lamont has offered to be interviewed by the Globe media concerning her rape. She is furious that Winston doesn't appear as she requested and gets revenge on him by implying in her closing comments that excessive force may have been used in attacking Roger Baptista. Winston goes to the crime lab to talk to Huber, the lab's director. Huber doesn't approve of Lamont's "At Risk" campaign either. Through a call to Tony, Huber finds out that Lamont had the missing case files sent to her weeks ago, but its unclear whether they ever reached her or not.
Sykes calls Winston with more information. She has found out that a forensic pathologist involved with the case died in a parachuting accident, and that it was put down as suicide. He had been investigating the death of Mark Holland, a detective with the Asheville police department, who had been run over by a train while lying on the tracks. Again, this was written off as suicide, although his widow Kimberley claimed he would never have committed suicide. Winston gets help from forensic scientist, Rachel, to analyse the threatening note the mysterious caller left for him at the diner, looking for hand writing indentations. Toby has a mysterious telephone conversation with an unknown person. It seems that Toby has lost something important that was meant to be left in a precise location where it would be found by the right person. Rachel and Winston manage to make out some indented writing on the note left for Win. It appears to be related to the stock market.