Bill Starr retired as an international information technology executive and enjoys training his new pup, Sam, and working for a national canine charity. His plans are interrupted when his exceptional goddaughter, Jayden, is savagely beaten by a star football player. She almost dies and becomes mentally and physically impaired.
When it becomes probable the ball player will escape arrest and prosecution, Bill decides to take action. He uses an artificial intelligence tool to gather information on the miscreant that ends with athlete's conviction and long incarceration.
The AI tool works well, and he targets child pornographers with success that catches the attention of the FBI because the tips they receive are flawless. Bill expands to search to the prevention of school shootings, police ambushes, and mass shootings. He moves on to include wrong convictions and unsolved crimes, which intensives FBI effort to find him.
Bill is bothered by horrible crimes that go unprosecuted because of legal or evidence problems and decides to take direct action. During one of his vigilante missions, he meets Lori, and they become close. She suggests they go after human traffickers and becomes an active vigilante with Bill. They have many close escapes and wounds.
Bill and Lori know the FBI is after them and are concerned about copycat vigilantes across the country. They decide to become an ordinary couple and turn their work over to others with a handbook of what they have learned as the FBI closes in on the entire group of vigilantes.