|“||That's an order, Marine!||”|
— Harrison in "The Fallen"
In his early years of adulthood, Scott was a sergeant for the U.S. Marines during the Vietnam War. He was very strict on his troops, though he never gave up on them and showed confidence in their abilities. When Rossi, one of the members of his troop, accidentally stepped on a Viet Cong booby trap, Scott refused to abandon him. He later took the credit of heroism for saving Rossi, when in reality, it was another one of his soldiers, Private First Class Anthony Hernandez, who saved the both of them by taking most of the booby trap's blast. He apparently didn't want to initially, but as the Vietnam War was unpopular with U.S. citizens and the country was also dealing with the Civil Rights Movement, the government needed someone who would be praised for his actions during that war and selected him. After the war, Scott was discharged and he moved to his hometown in California, to start a new life. There, he had at least one marriage (which would later be failed), with whom they had at least one child, a son named Thomas. His relationship with his family became heavily strained when he became a drunkard. About five years prior to "The Fallen", he was struck with poverty after being fired from his construction job, which he blamed on his age, though it is implied that it was because of his alcoholism. Scott went to Santa Monica and came to be familiar with several other homeless people, including a woman named Sarah Mapes and a sketch artist named Jeremy.
Scott reunites with Rossi at a homeless shelter when he and his team come to Santa Monica to investigate a string of killings targeting homeless people. The two talk and Scott tells Rossi about his life after the Vietnam War ended. When Rossi turns his back on him while saying that the two of them should get together more often, Scott walks away. He later reappears, helping the BAU identify the fourth victim of the killings, which happens to be Jeremy. He then helps the team spread their profile of the unsub to the homeless community. The following night, Scott rests himself between dumpsters when he hears a man approach Sarah Mapes, asking if she needs assistance. Sarah declines, to which the man starts saying that she has a disease. Scott recognizes the man as the unsub, just as the man attacks Sarah. In return, Scott defends Sarah but is eventually subdued by the man who then makes his getaway with her. He later recounts the encounter to Rossi at the police station.
The BAU identify a suspect, Chad Mills, and arrive at his residence, where they find Sarah alive, but no sign of Mills anywhere. Meanwhile, Mills is able to find Scott and forcibly abducts him, accusing him of "ruin[ing] everything". Mills takes him to a warehouse, where he had previously saved several vagrants from an electrical fire but contracted tuberculosis as a result. Scott taunts Mills when he begins to cough, then Mills douses him in a flammable fluid, just as Rossi, JJ, and Morgan burst in and hold Mills at gunpoint. However, Scott orders the three to step down, which they do, but they reenter the warehouse through a different route and Rossi is able to free Scott. Mills, standing in the flammable liquid, sets himself on fire and dies. Scott then admits to Rossi about him taking the credit for Hernandez's sacrifice. By the end of the episode, he and Rossi watch as Hernandez's grandson, also named Anthony Hernandez, is granted the medal his grandfather deserved. Rossi also introduces Harrison to New Directions, a charity organization that helps war veterans get back on their feet, so he can get the help he needs and start over. In the final scene, Rossi is seen mentioning both Scott and the original Hernandez in the dedication page of his latest book, Evil Never Rests.
Sometime prior to the episode, Scott learned that he was dying of bone cancer. He decides to leave New Directions, sending Rossi a pistol with a Vietnam War logo on its grip. Knowing that such a purchase would technically drain out the money he has, Rossi realizes that something is wrong when he learns that Scott hasn't been at his work in the past two days, and decides to head over to Los Angeles to visit him, while the rest of the BAU investigates a case. Rossi later learns from an employee of the organization that he has less than 24 hours to find him before he is dropped from their list. He later finds Scott at his old apartment, which he used to frequent in when he and his troop were stationed in Camp Pendleton, and Scott yells at him. When Rossi asks what happened to him, he replies that he "came a long way for nothing". Rossi then finds that Scott was attempting to drink again. He then tells him that he doesn't know why he was spiraling down again when he was doing so well, saying that he was at the end of his road.
Scott and Rossi later eat Chinese food, to which Scott reveals that he saw his son Thomas living nearby. He then tells Rossi that he tried calling him, but Thomas immediately rejected his attempt at reconciliation, but not before Scott realized through the call that he has a grandson. Rossi then takes Scott over to Thomas's home, intending to get the two of them to meet again, but Scott denies that it will ever work. Rossi then decides to speak to Thomas alone, telling him that Scott didn't send him and that he just wanted to talk to him. He then learns that Scott's alcoholism humiliated Thomas during his childhood. Thomas tells Rossi that he doesn't hate his father, but that he just wants to protect his family from the same humiliation he experienced. Rossi goes outside and tells Scott that his relationship with his son built itself over time and that it won't fix itself overnight. The next day, Scott has been shown to return to New Directions. Rossi wishes him farewell and is about to leave when he sees Thomas, his wife, and their son meet up with Scott, and Scott's grandson shakes his hand as he smiles.
It was revealed that Scott died of bone cancer a day prior to the events of the episode. He never disclosed his new affliction to Rossi prior to his death. A funeral for him was hosted by Rossi and was attended by him, his daughter Joy Struthers, Thomas, Thomas's wife, and son, and the surviving members of Scott and Rossi's old squad in Vietnam. Scott also appeared in a flashback during the Vietnam War, during which he personally gave Rossi a Purple Heart award while he was bedridden from a serious injury.
- In an interview with Doug Aarniokoski, Meshach Taylor, the actor who portrays Scott, was revealed to have been a friend of Joe Mantegna, who portrays Rossi and directed "The Fallen", for 44 years. After Taylor's death, Mantegna requested to direct an episode in Season Ten as a tribute to him.