Rebecca Shaw first appeared in Port Charles during a crisis at General Hospital. Despite the shorter hair and heavy eye makeup, her resemblance to the late Emily Quartermaine was unmistakable. Rebecca insisted that she had never heard of Emily nor was she related to the young woman whom everyone seemed to view as a saint. Few believed Rebecca's claims, especially after she went through a breast cancer scare; Emily had nearly died from breast cancer.

Meanwhile, a grieving Nikolas Cassadine became fixated on Rebecca, which Rebecca seemed to resent. Rebecca briefly dated Lucky, the only person who seemed to accept Rebecca for whom she was. Nikolas, certain that Rebecca was as attracted to him as he was to her, resented his brother's relationship with Rebecca, so he decided to teach Rebecca and Lucky a lesson. Nikolas invited Elizabeth to Jake's and then proceeded to flirt with her in front of Lucky and Rebecca. Elizabeth realized what Nikolas was up to, so she played along with it. When Nikolas kissed Elizabeth, Lucky and Rebecca grew jealous.

Rebecca was forced to admit that, despite her better judgment, she cared out Nikolas. While Lucky and Elizabeth rekindled their romance, Nikolas and Rebecca embarked on a new relationship. However, as Rebecca fell in love with Nikolas, her past returned to haunt her. It was revealed that Rebecca Shaw and Luke's newfound son, Ethan Lovett, had met each other in an airport. When they discovered that they were both headed to Port Charles, they began to talk. Instead of going to Port Charles, Ethan and Rebecca became lovers and then hatched a plan to swindle the Quartermaines and Nikolas out of a large chunk of their considerable fortunes.

Rebecca was angry because she had learned that she had been adopted out while her twin sister had remained with their parents. Further adding to her fury, Rebecca discovered that a wealthy family had later adopted Emily and then she had married a rich prince. Rebecca felt that she was entitled to a share of the Quartermaine and Cassadine fortunes because she had been cheated out of a similar life as Emily's. After months of careful planning, Ethan and Rebecca arrived in Port Charles to put their con into motion.

Eventually, Rebecca and Ethan arranged for everyone to find out that Rebecca had been Emily's long lost twin. It was crucial to their plan. The Quartermaines were delighted by the news. Monica and Edward accepted Rebecca with open arms while Nikolas fell more in love with Rebecca; unfortunately for Rebecca, so had Ethan. Ethan grew jealous of Rebecca's attachment to Nikolas, so he threatened to expose everything. Rebecca begged Ethan to reconsider because she feared that she would lose Nikolas. Ethan agreed to keep quiet, but it was too late. Lucky had learned of the truth and had decided to tell Nikolas.

Nikolas was shattered by the betrayal. He decided to hurt Rebecca as deeply as she had hurt him. Nikolas pretended to forgive Rebecca, but it was a ruse designed to set her up for a painful downfall. Ethan tried to warn Rebecca not to trust Nikolas, but she refused to listen. During this time, Nikolas turned to his best friend, Elizabeth, for advice. Nikolas and Elizabeth realized that the attraction that had led them to kiss in Jake's months earlier had grown, not diminished. Nikolas and Elizabeth embarked on a torrid affair. As his love for Elizabeth grew, his desire to punish Rebecca lessened.

Nikolas decided to break things off with Rebecca because he couldn't ignore his feelings for Elizabeth. Rebecca was devastated, but determined to salvage her relationship with Nikolas. One night, she returned to Wyndemere with the intention of working things out with Nikolas, but she found him in the turret room making love to Elizabeth. Rebecca was livid, but she decided not to confront the lovers.

Rebecca spent several weeks threatening to tell Lucky about Elizabeth and Nikolas' affair. She then blackmailed the lovers to step aside, so that she could seduce Lucky. Rebecca decided that Lucky deserved someone better than Elizabeth. Lucky saw through Rebecca's attempt to seduce him away from Elizabeth, so he decided that Rebecca needed to understand the close connection that Lucky, Elizabeth, and Nikolas had shared with Emily. When Rebecca realized how deeply they had loved her sister, Rebecca decided to keep quiet about Nikolas and Elizabeth's affair. When Monica offered to send Rebecca abroad, Rebecca accepted.

As Rebecca boarded a plane bound for Paris, she sat down next to a passenger named Aaron who bore a striking resemblance to Emily's love, Zander Smith. Aaron's company had transferred him to Paris. Rebecca and Aaron seemed to hit it off immediately.