Brook Lynn Ashton was named after Brooklyn, New York, where her mother and father had spent many happy times together. However, at the time of her birth, Brook's parents were estranged. Lois had returned to her family in Bensonhurst after she realized she didn't want her daughter growing up around the Quartermaines. Her feelings were cemented after Ned failed in his attempts to make Lois and their record business his first priority. He returned to ELQ, and Lois returned to her family. Lois took Brook to meet Ned a few months after she was born. Although Lois claimed she hadn't shown up to reconcile with Ned, it was clear Lois and Ned were still in love with each other. But after she overheard him blackmailing his cousin Justus, Lois left town with her daughter.
Ned saw his daughter on birthdays and introduced her to Chloe when he was married to her. Brook adored Chloe and was not thrilled to learn several months later that Alexis had become Ned's new love. She later grew to like Alexis, but couldn't understand what was happening when Alexis left her father at the altar.
Brook returned to Port Charles in early 2004, using Lynn as her name. After haunting L&B's studio with her talented singing voice, she became friends with Georgie and Dillon, who was unaware that he was Lynn's uncle. Impressed by her voice, they persuaded her to record a demo tape. But Lynn remained adamant that she only sang for the joy of it and didn't want to profit from it, which was something her mother wanted her to do. Lynn's true identity and ties to the Quartermaines were revealed after a man claiming to be her father attempted to take her home to her mother. She escaped by stealing his car, but Dillon later turned them in to the cops, and they wound up back at the Quartermaines'. Lois wanted to take Brooke back to Bensonhurst with her, but Ned persuaded her to let Brook stay, and to stay in town with Brook.
Lois repeatedly tried to convince Brook that she should sing professionally, but each time they ended up in a fight. Seeing how hard Brook fought her mother, Ned took a different approach. He persuaded her to sing with him just for fun. But she remained strongly opposed to singing professionally. She was even willing to let Sage sing one of her songs rather than sing it herself.
Mother and daughter had the same idea of delivering roses to Edward after Lila died. Each of them regretted the fact that Brook had never gotten to know Lila. Brook finally sang for a crowd at her great-grandmother's funeral. Later she misinterpreted the situation when Lois tried to convey how proud she was of her daughter. Believing that Lois wanted to capitalize on the event, Brook yelled at Lois, who took off, hurt by her daughter's words.
Brook's relationship with her mother continued to go poorly as Lois became involved with Lorenzo Alcazar. Brook hated that her mother would date a thug when Brook was always told not to. In an attempt to give her mother a taste of her own medicine, Brook began getting cozy with Diego, Courtney's foster child. Diego had made his desire to work for Sonny obvious to anyone who would listen, and Lois wasn't a fool. Diego and Brook grew closer when Brook walked in on her mother and Lorenzo shortly after the two had made love. Enraged, Brook ran away with Diego, where the two escaped to Mexico to find Diego's sister, Maria.
Georgie and Dillon accompanied Diego and Brook, and the four were arrested when Maria denied knowing Diego and let her fiancÚ arrest the group of teenagers. She later had them released and warned Diego to get out of Port Charles. Brook and Diego then began their mission to discover why Maria didn't want Diego in Port Charles. Working together, they determined that Sonny must have killed Diego's father, and Diego decided to find out why. Dressing as a delivery girl, Brook attempted to divert Max's attention while Diego tried to break into Sonny's apartment. Sam caught the two before they could enter the apartment. Jason agreed to help Diego find out if Sonny had anything to do with the murder of Diego's father, and Courtney arrived to take the two home.
Diego and Brook Lynn didn't last long, because he soon developed an interest in Maxie Jones, leaving Brook Lynn out in the cold. After graduating from high school, Brook Lynn enrolled at Port Charles University -- and ended up having Maxie as a roommate. After being drugged at a party, Brook learned there were nude pictures of her circulating on the Internet and elsewhere. She began to suspect that Diego was her stalker, but he kept coming up with all the right answers for every one of her questions. Ultimately, Brook learned that her suspicions were right: Diego had indeed been stalking her as payback for what Brook Lynn and the others had done to Sage.
A short while later, Brook Lynn decided to leave Port Charles and join her mother in New York so that she could pursue a music career.
In 2010, Brook had been cut off from her trust fund after getting in trouble for credit card fraud. Brook refused to turn to Edward and Tracy for help because they wanted her to enroll in college and study business, instead of allowing her to pursue her music career. Carly caught Brook hustling people for money in the park, so Carly offered Brook the opportunity to make quick money in exchange for seducing Dante away from Lulu.
Brook Lynn agreed to seduce Dante. Carly hired Brook to sing at the Metro Court as a cover story to explain their meetings. Dante was excited to see Brook, and Lulu was immediately jealous of their friendship. Carly arranged for Brook to move in across the hall from Dante, which increased Lulu's insecurities. Brook made herself at home in Dante's apartment, and she reminisced about the "old days" in Bensonhurst with Dante and his mother Olivia.
Although Brook Lynn planned to seduce Dante, she was interested in Johnny Zacchara and flirted with him. Johnny was involved with Olivia, and Carly warned Brook to stay away from him. Carly demanded that Brook make progress with Dante, and the two women staged an argument for Lulu's benefit. They planted the idea in Lulu's head that Dante was destined to cheat because, as Sonny's son, cheating was a part of his DNA.
Brook Lynn arranged for Dante to find her locked out of her apartment, wearing only a towel. When Dante did not make a move despite Brook's obvious interest, Brook realized he truly loved Lulu. Brook resorted to drugging Dante's drink, and she arranged for Lulu to find them in a compromising position. Lulu was upset with Dante, but she quickly realized he had been drugged. Brook knew she had been caught, so she told Lulu about the deal she had made with Carly. Things backfired for Brook when Carly was able to turn the blame back onto Brook.
Brook Lynn was alone and broke with a damaged reputation when she almost turned to the Quartermaines for help. Nikolas Cassadine provided her with another option. He hired Brook Lynn to be his date for business functions. She moved into Wyndemere and accompanied Nikolas to various events. They also attended Luke and Tracy's wedding together, as well as Brenda and Sonny's wedding.
Just as Brook Lynn began to develop romantic feelings for Nikolas, Liz made it clear she was also interested in a relationship with him. Nikolas and Liz had a child together named Aiden, and Liz used their son to get closer to Nikolas. Every time Nikolas and Brook started to get close, Liz interrupted them. When Liz arranged a special dinner for Nikolas, Brook conveniently got a flat tire in front of Liz's house. Nikolas thanked Brook for causing his evening with Liz to end early.
Nikolas and Brook Lynn admitted they had feelings for one another and made love. Liz walked in on an intimate moment between them and decided Aiden could not spend time at Wyndemere if Brook was present. Nikolas stood up for Brook and asked Liz to leave.
When Liz's son Jake was killed after being hit by a car, Nikolas knew he needed to focus on helping Lucky and Liz grieve instead of on his relationship with Brook Lynn. Nikolas encouraged Brook to pursue the offer she had to tour with a Latin band. Nikolas and Brook both wished the timing and circumstances had been different and parted as friends. Brook Lynn moved out of Wyndemere and away from Port Charles to pursue her music career.