In Mistress by James Patterson, newspaper editor Benjamin Casper gets caught up in the danger of political blackmail. He tries to prove that his friend, Diana Hotchkiss, did not kill herself. As Ben delves deeper into her death, he learns Diana is not dead at all. Instead, she is part of a scheme to rebuild the old Soviet Union. Along with his friend's true identity, Ben also learns the truth about the death of his mother, the role his father played in this murder, and why his father set him up as the killer.

As the story begins, Benjamin has just left Diana’s apartment when he sees her fall from her balcony. Ben does not believe that his friend killed herself and decides to find out the truth. He attends Diana’s visitation in her hometown of Madison, Wisconsin. On his way home, his plane crashes, an act that he believes was meant to look like an accident but was instead an attempt to kill him. He tries to hide out at his cabin on Lake Anna only to have armed men try to kill him there as well. His friend, Ellis Burk, shows Ben crime scene photos of Diana’s murder, which help Ben know that it was not Diana who was killed. Ellis tries to help Ben in his investigation but is shot and killed.

With the expertise of a professor of Russian descent, Ben begins to piece together the plans the Russians have to blackmail the President of the United States into allowing them to invade the Republic of Georgia, the first step to rebuilding the old Soviet Union. Ben realizes that Diana was not killed. A friend who had stayed at her apartment was killed in Diana's place. It was Diana who filmed the blackmail tape, a sexual encounter between herself and the First Lady, that the Russians hope to use against the President.

It is not until after he is arrested that Benjamin realizes that the deputy director of the CIA has not told the President what is going on with the Russians. After Benjamin tells the President what has happened, the deputy director is forced to hand in his resignation. Ben is absolved of any responsibility in any of the crimes.