Maggie showed up on the scene in Genoa City as a police detective, mostly investigating the Drucilla Winters/Carmen Mesta cases. She has disclosed that her father was also a cop.
Paul Williams managed to track Sheila to Argentina in October 2006 and discovered that she had undergone plastic surgery to look like Phyllis Summers, then had killed the plastic surgeon. Paul, later in October, discovered her buying baby things in Genoa City, and followed her to a warehouse where he trapped her in the cell she had constructed with the intention of imprisoning Lauren and stealing her baby Fen. He made her pose for a death photo at gunpoint and made up DNA samples to convince Lauren and Michael that she was killed when struck by a car in Argentina. Paul also let Phyllis and Nick know. Paul kept her imprisoned there undetected until December when Michael put a tracking bug on Paul's car and caught Paul bringing her food. Michael picked the lock and was shocked to discover "Phyllis" behind the bars. Paul appeared and tried to convince Michael that it was really Sheila, but it took a cell phone call to the real Phyllis to convince him. Knowing the authorities can never keep her contained, Paul and Michael shared a secret and the dilemma of what to do with her. Meanwhile Lauren and the real Phyllis were bonding through their pregnancies as she helped Lauren get through her postpartum depression and anxiety attacks.
Detective Maggie Sullivan and Paul Williams began dating, and in her curiosity about Paul's frequent absence "on a stakeout" she tracked him by his cell phone to the warehouse. Sheila conned her into believing she was Phyllis, Maggie let her loose, then Sheila shot her with her own gun. Paul arrived later and was trapped in the cell too by Sheila when he came to Maggie's aid. Sheila then went to Phyllis's, tied her up and waiting for Lauren and baby Fen to arrive, taunting Phyllis about how great it would be to take over her life with her hot husband and new baby. After Lauren arrived she was tied up, and Sheila took Phyllis and babies Fen and Summer to a retirement home where she had an apartment. Michael eventually rescued Paul and a near-death Maggie from the warehouse cell, and they rescued Lauren. While Michael and Paul followed Sheila's walkie-talkie signal which she planted to lure them elsewhere, Nick and Lauren with the aid of Kevin enhanced the background noise from her latest taunting call. Nick realized where they were and while they tried to find Paul, Lauren snuck out with the gun Paul had given her for security. Lauren found the apartment, broke in, and confronted the two Phyllises. Phyllis managed to convince Lauren she was the real one, and Lauren shot Sheila dead! Her dying words still taunting Lauren that she would never be rid of her and she had shot the wrong one, lead us to believe that this may have yet been another pawn of Sheila and she may still be out there and a threat. Phyllis was livid with Michael and Lauren for endangering her and her baby Summer, but they eventually reconciled. Maggie recovered from her gunshot wound and did not tell the police about Paul or Michael holding Sheila in that cell, so they were not charged.
Paul and Maggie continued to be involved, and Maggie underwent quite a transformation from her usual "plain Jane" cop persona into a very attractive woman. She and Paul had great chemistry, and was a welcome addition to Genoa City and Paul's life. They became involved in the investigation of the Glo By Jabot tainted face cream scandal, the murder of Ji Min Kim, and were suspicious of the death of D.A. Will Bardwell. But Maggie disappeared from the show with no explanation.