Riley's father, Paul Desario, was the Sheriff assigned to supervise Glenport Village, an experimental community designed to house mostly convicted sex offenders, having held the job for six years. She and her younger brother Danny were raised solely by their mother after their parents divorced, but six months prior to Pariahville, she died of unspecified causes and the two were transferred under the care of their father. As a result, they had to live in a community just outside of Glenport Village, to a point where she sometimes had to pass through it, which disturbed her. Aside from that, Riley managed to adjust to her new surroundings and came to befriend, among others, Adam Jenkins, a schoolmate who lived in or near Glenport Village, and Matt Franks, the young next-door neighbor. She began participating in school activities, most notably trying out for the cheerleading team at her local high school.
Riley is first seen coming to the police station during a case, where Paul introduces Hotch to his children. Hotch shakes hands with Riley and Danny. They then leave the police station and walk with Adam. Riley talks about how she and Danny had to move in with Paul when their mother died. Adam says that he understands, then invites her to a friend's party, but she says that Paul would not let her go because of the neighbors. Later, when Paul drives back home, he asks Riley and Danny what they want for dinner tonight, then tells Riley to look over Danny's homework. When they step inside, Riley asks Paul if she can go to Adam's party. Paul asks Riley where it is, and she replies that it is not far. Paul allows her to go, but on the condition that she has to first stay with Danny until Paul finishes with his rounds and that she has to be home by 10:30. Riley becomes excited, hugs him, and says that he is the best father ever. Later, Riley and Danny come to the police station; Paul takes them to his office and says that they are going to spend a night there for their own safety. He then apologizes to Riley for not letting her go to the party, explaining that it is because of the recent murder of Victoria Taylor and he wants Riley to be safe in the station, but this frustrates her. Afterwards, Riley calls Adam and tells him that she can't go out; Adam tells her to sneak out. Danny tries to stop her from going, but he eventually allows her to on the condition that he use her computer for two weeks.
Later, as Riley is driven to the party by Adam, she gets suspicious when he drives past it. Adam stops the car and tries to have sex with her, but she pushes him away. She then tells him to drive her back to the station, but an enraged Adam refuses and kicks her out of his car. As Riley walks home, Matt appears with his car and offers Riley a ride back, which she accepts. Suddenly, Matt drives past the police station, knocks her out, and drives to her house. Riley regains consciousness and finds herself wearing a cheerleader uniform. Matt holds Riley at knifepoint and explains his motive when she asks. Riley realizes that Matt is responsible for the murders and plays along with his fantasy in order to survive. She first lures Matt into Paul's bedroom. When Matt tells Riley to do her routine, she says that she needs her pom-poms. She approaches the closet and tries to grab a shotgun inside, but a suspicious Matt stops her and asks why her pom-poms are in her father's closet. When she tries to grab the shotgun, Matt subdues her and the both of them struggle. During the struggle, the shotgun goes off and hits the ceiling. Riley kicks Matt, but he overpowers her, knocks her down, and presses her face against the window. Just then, the BAU appears outside and an enraged Matt holds Riley at knifepoint. Morgan and Lewis go into the house and try to talk down Matt. Lewis manages to lower Matt's guard down by asking him about his parents; she then shoots and kills him. Afterwards, Riley is reunited with Paul, who comforts her.