Pilar Domingo's introduction to Oakdale was shrouded in mystery, on many levels. As Mike Kasnoff was building up his stock racing career, he was also helping out his friend, Lily Walsh, who was investigating a man named Umberto Malzone, who may have been responsible for the death of her husband, Damian. Not able to get to Malzone, Lily discovered that he had an employee named Diego Santana and got close to him in order to get the goods on Malzone. Amidst this intrigue, Mike met a beautiful woman named Pilar who was stranded on the side of the road when her car broke down. Gallantly offering to help her fix her car, Mike became quite taken with Pilar who recognized him from the stock car circuit and teased him about losing to a driver named Domingo, a driver that Mike though took too many risks on the track. Liking Mike, Pilar agreed to give him her number, if he beat Domingo in the next race. However, to Mike's chagrin, and Pilar's amusement, he lost again to Domingo. Later, after losing a third race, Mike made a startling discovery--Pilar was Domingo! Finding out that she was Domingo, Mike lit into her for her reckless driving. Although she was certain that he was mad because he lost to a woman, he argued that she took too many unnecessary chances to win and was certain someone would get hurt. The following week, Mike's fears were confirmed when during a race, Pilar's car crashed and she was rushed to Memorial. Frantically trying to save her life, the doctors discovered that she had a rare blood type and went on a desperate search. As the doctors worked to save Pilar, Diego was at the hospital looking troubled and torn. Finally, he went to the doctors and told check his blood for compatibility. To everyone's relief, it was a match and Pilar's life was saved.

Not long afterward, Mike overheard Dr. Susan Stewart thank Diego for his blood donation and became suspicious. Doing some investigating, he found a picture in Pilar's locker that was identical to one Diego had in his apartment. Putting more clues together he made shocking discovery--Pilar was Diego's sister! Meanwhile, Diego himself was sitting at a sleeping Pilar's bedside as she recovered from surgery. Believing her to be heavily sedated, a shaken Diego talked to Pilar about their childhood and things he'd done. After praying to God for her to live, Diego left. Just then, Pilar woke up, having heard everything; including Diego's confession to having caused the plane crash that killed Damian Grimaldi. In shock over the revelation, Pilar became hysterical, almost blabbing the truth to her doctor, but before she had a chance, Diego walked in the room. Alone with her brother, a shaken Pilar asked him point blank how he became a murderer. Although he tried to deny it, Pilar wouldn't hear it and started to scream hysterically "MURDERER!" However, Diego got her to hush up and calm down.

Later, Pilar received a visit from Mike. Sensing how upset she was, Mike asked what was bothering her, telling her that no one could hurt her since they were alone. Feeling safe, Pilar told Mike what she and Diego had always agreed not to reveal--they were brother and sister. Afterwards, to her shock, Diego went to her room and demanded to know why she betrayed him. Not understanding how he could know what she told Mike, she was horrified when Diego told her that he hid a tape recording device in her room. Scared for her brother, Pilar pleaded with him to leave Oakdale with her. Diego refused; he wouldn't leave without the woman he loved--Lily. While she feared for her brother and what he might do, Pilar received another visit from Mike who asked if she knew a man named Umberto Malzone. Telling Mike she knew him, she also told him that he wouldn't kill again, she was sure of it. However, Mike was unconvinced and badgered her until she became so rattled she changed her story and said she didn't know him.

Not long afterward, things would finally come to a head. Scared of what an agitated Pilar might say, Diego kept her drugged. When Mike realized what was happening, he convinced Pilar to stop taking the pills she was being given. Trusting Mike, she complied and once clear-headed, she tried to escape the hospital. Unfortunately, she was stopped by Diego himself. Again Pilar tried to reason with her brother, telling him that Lily would never forgive him if she learned he was Umberto, a murderer. Again Mike was able to get to Pilar and convinced her that Diego was a dangerous man, citing Diego's recent rape of Emily Stewart. Hating her brother for the crimes he had committed, Pilar made plans to escape again and go to the police. However, before she had the chance, Diego was killed on his wedding day, apparently by his new wife, Lily! Lily became the prime suspect when it was learned that she overheard Pilar and Diego's argument, thus learning that Diego was responsible for Damian's death. Totally devastated by Diego's death, Pilar demanded that Lily pay. Although Pilar had the ability to help the police go easy on Lily, given Diego's crimes, this time Pilar refused to acknowledge that Diego had done anything wrong. In denial, she placed the blame of his death entirely on Lily, making her the cause of his ruin. After painting Lily as a psychopath who killed Diego in cold blood, Pilar made sure that Lily wouldn't get parole by staging an attack so that the police would think Lily attacked her. Although Mike tried to get Pilar to see reason, she refused and continually defended her brother to everyone. Consumed with rage over her brother's death, Pilar started taking even more chances on the race track, appearing suicidal. Concerned for her well-being, Mike confronted her and following a heated exchange she finally broke down and revealed that this was all her fault since she wished her brother dead. Finally able to see her brother for what he really was, Pilar agreed to help Lily. Later, she and Mike left Oakdale together to race in Spain.

Seven years later, Pilar would return to Oakdale with a secret agenda. Teary-eyed, Pilar arrived at Mike's doorstep (Mike had returned to town years earlier), apparently the victim of a mugging. Concerned, Mike got Pilar to a hospital and upon her release, he asked her to stay with him since she'd confessed that she'd been beaten by her abusive lover who was threatening her life. Although Mike believed Pilar's story, his ex-fiancée, Katie Peretti, was very suspicious and was certain that Pilar was out to hurt Mike. While Katie tried to convince Mike that Pilar was lying and out to hurt him, Pilar succeeded in playing the innocent and put-upon victim. However, unbeknownst to everyone, Katie was right--Pilar's abusive past was a ruse to get Mike. Conspiring with a man named Russ Terrier, Pilar tried to set it up to look as if he was stalking her. Unfortunately, Katie was certain that Russ and Pilar were working together. Finally things went awry and Mike discovered Russ and, despite Pilar's pleas, he had him arrested. Though a scared Russ was adamant about Pilar getting him out of jail, she convinced him to sit tight because she'd take care of everything. Things finally started looking well for Pilar when, during a confrontation with Katie, she was able to stage it so Mike would think Katie was attacking her. Her credibility gone, Katie was sent to a mental hospital. Afterwards, Pilar decided to taunt Katie by taking a picture of herself with Mike and showing it to Katie.

Unfortunately, Pilar's overconfidence would be her downfall when Mike discovered what she'd done. With this revelation, Mike suddenly realized that Pilar wasn't the sweet, innocent girl she pretended to be. Realizing that Katie was right all along, Mike wrote Pilar out of his life. At the same time, Katie was rescued from the hospital by her estranged husband, Simon Frasier. It was then that Pilar's true motive for coming to town was discovered--Simon hired her to get Mike away from Katie. While Simon was getting what he wanted, Katie, Pilar was left in the lurch since Mike no longer trusted her and wanted nothing to do with her. Angry that Katie ruined everything for her, a truly demented Pilar decided to get even by kidnapping her to the boathouse near Mike's home and murdering her. Unfortunately for Pilar, she made a fatal error by giving Mike (who'd called her cell phone) a clue as to their whereabouts. Mike's arrival was all the distraction Katie needed to wrap Pilar in a fisherman's net as a means to get away. Unfortunately for Pilar, Katie's efforts caused her to fall on her own knife.