Joy was born as a result of the short-lived marriage between Rossi and Hayden, a French diplomat. The two had divorced prior to her birth because of the demands of their respective jobs, with Rossi being unaware of Hayden's pregnancy at the time. As a result, Hayden remarried, and after Joy was born, she believed that her stepfather was her biological father. In 2006, while attending New York University, Joy was attacked by a man who attempted to rape her, but she managed to fight him off and escape. Because she was drunk at the time, she decided to leave the incident unreported, realizing the police would never believe her. A week later, another college student named Kathy Miller (who she had one class with) disappeared, and she became guilty, believing the abductor to be the same man who attacked her. She moved to San Francisco, California, and became a true crime writer, much like her biological father. She wrote at least two books, one about the Zodiac Killer, and another that tanked in sales. Joy also married an Italian man and had a son with him, named Kai. In 2014, when her stepfather came down with cancer, he confessed the truth about her real lineage before dying. As a result, Joy confronted Hayden about it and learned that her father was indeed Rossi. She then began stalking him, wanting to learn more about him.
Joy first appears sitting in a car parked behind Rossi's own. As she does, she looks at Rossi's file next to her. She then proceeds to follow Rossi to a coffee shop. When he steps outside, he approaches her, gives her coffee, and tells her that when he saw her following him the day before. Then, Rossi asks Joy if she is a private investigator, but she doesn't give him a straight answer. He then asks Joy for the identity of her client, but she doesn't respond and leaves. The next day, Joy visits the BAU headquarters, which disturbs Rossi. Confronting her, Rossi demands to know what Joy is doing in the building. He then tells her that he knows she is not a private investigator, but a reporter trying to be a novelist. Joy says that she needs to see him. When Rossi tells security to escort her out, Joy reveals that she is his daughter. She tells him about her mother and how she figured out Rossi was her father. He finds it hard to believe, but Joy explains that she was scared. Rossi then tells Joy that they will straighten it out later and instructs her to leave her info at the front desk.
After solving a case, Rossi, deducing that Joy is indeed his daughter, tracks her down at the airport. He tells her that she flew all the way to Quantico to meet him and figures that she has a few questions to ask him. He proceeds to explain to Joy why he didn't stay with Hayden: they had a complicated relationship because Rossi was moving up in the ranks of the FBI and Hayden was a diplomat. Joy says that it is not good enough of an explanation. Rossi adds more, saying that with Hayden meeting with dignitaries and traveling to different countries, he couldn't handle it. Instead of confronting the situation head-on, he pushed Hayden away and wasn't sure he wanted to continue their marriage. Joy reveals to Rossi that he was the love of Hayden's life; Rossi replies that he was never told about Joy's existence by Hayden and that he would have known about her otherwise. Joy then informs him that she has a son who is running a fever, and a husband who is Italian. Rossi would like for Joy to have some company for the weekend, to which she replies that she likes the idea of getting to know Rossi, even calling him "Dad". Afterwards, they both board the plane.
Joy reappears in the episode. When Rossi finds out that his former squad commander during the Vietnam War, Harrison Scott, died of lung cancer the day before, he flies to Los Angeles, California, and calls Joy. She tells him to take all of the time he needs and says that she and her family will be fine. Afterwards, Rossi tells Joy that he will call her tonight. Instead, however, she flies over to Los Angeles, surprises Rossi, and tells him that there are times when families should be together. Rossi is glad that Joy came to give him some comfort. At the end of the episode, Joy attends Scott's funeral along with Rossi, Scott's family, and members of Scott and Rossi's former squad.
Joy calls Rossi and tells him that she needs to talk to him. She comes to the BAU headquarters and asks her father to look at the investigation of five missing college students, including Kathy Miller and one Bahni Desai, who disappeared recently. Joy explains that she first uncovered Kathy's disappearance in 2006, followed by the others. Rossi tells Joy that they will find Bahni. After Sam Burnett, a suspect, is released, Joy becomes frustrated, but her father tells her that Burnett didn't match the profile. Rossi then adds that he is doing everything he can to find Bahni, and she replies that she needs some air. The following night, Joy goes to meet Burnett in an alley, secretly using her phone to record their conversation. She asks Burnett about Bahni's abductor and what he did to her. All of a sudden, Burnett shoves Joy to the wall, panicking her. He claims that he was showing her what the man did to Bahni. When Joy says Kathy's name, Burnett admits that he hadn't heard the name in a long time. Then, the BAU show up, having tracked the both of them down, and arrest Burnett.
Afterwards, Rossi asks Joy what she was thinking. She explains that she knows that Burnett abducted Bahni, but Rossi says that Joy is a parent and that she shouldn't be meeting up with murder suspects in dark alleyways; calling her actions stupid before asking her how she would feel if her son Kai did the same. She then tells him about her unreported attempted rape. Later, the BAU find Bahni and identify her real abductor, a man named Tom Larson. After Tom is arrested and Bahni is rescued, Rossi tells Joy that Burnett has been tied to three of the four disappearances she had been investigating, including that of Kathy. When she apologizes to him about meeting up with Burnett, he says that Joy survived a traumatic event and that she needs to talk to somebody like him. When Joy abruptly gets a call from her editor, she introduces herself as Joy Rossi, which surprises her father. After she hangs up and he asks about it, she explains that she didn't get to use the surname of Rossi growing up, so she decided to try it as a new byline. Afterwards, Joy and Rossi hug each other.