Llanview University student Hannah O'Connor met Cole Thornhart when they were paired up on a class project. Hannah told Cole she had recently broken up with her boyfriend and had gotten involved with an older man, a teaching assistant at Llanview University, but he had dumped her after they had sex. Hannah tried to kill herself by swallowing a bottle of pills, but Cole found her and helped her recover. Hannah then told Cole that the teaching assistant who had dumped her was Robert Ford, who had recently bedded an even younger Langston Wilde. When Hannah confronted Ford at the diner, in front of Cole and Markko, Ford convincingly accused her of stalking him after he told her he wasn't interested in pursuing a relationship.

Hannah and Cole began spending more time together, and Starr suspected that she was attracted to him. One day Hannah spilled coffee on her blouse while visiting with Cole, and Todd barged into the apartment to find Hannah wearing only her bra. Todd went ballistic on Cole, accusing him of cheating on Starr. After Todd left, Hannah and Cole were hugging when Starr walked in. Cole explained what had happened with Todd but Starr took her father's side, angering Cole. Later, Cole learned his mother Marty had been pushed down the stairs, causing her to lose her unborn baby, and he told Starr that Marty suspected Todd. The two argued, as Hannah eavesdropped. After Starr walked out, Hannah told Cole that she had seen Todd push Marty down the stairs, and Cole beat Todd so severely that he nearly died. Starr accused Hannah of lying and later suggested that Hannah may have pushed Marty herself to pin the deed on Todd and split them up. Cole, locked up for beating Todd, refused to believe Hannah would so such a thing, causing a further rift between him and Starr.

Hannah happened upon Starr in the park, talking to a handsome young man named James Ford, and snapped their picture. Later she showed the photo to Cole, who had been released from jail on bail, and told Cole that Starr was cheating on him. Hannah took Cole to a home in Delaware where she said Starr and James had gone, only it was really her grandparent's beach house. Hannah planted Starr's diploma and an open condom wrapper in the bedroom, leading Cole to believe Hannah's story. Hannah and Cole nearly had sex before Cole stopped it. When the police arrived, wanting to arrest Hannah on charges of bludgeoning Robert Ford, Hannah told Cole the police were actually after him for jumping bail and they went on the run. They ended up at a hotel in Maryland, where Cole discovered Hannah had been lying to him. Hannah confessed to lying about Starr and James and even admitted that Todd didn't push Marty down the stairs, but she continued to deny having pushed Marty or trying to kill Ford and told authorities she would name Marty's attacker if she got immunity.

Hannah called attorney Eli Clarke, who it turned out was actually behind both crimes. Eli threatened to kill Cole unless Hannah admitted to the crimes. Hannah faked a mental breakdown while in custody and switched her story, claiming she had pushed Marty and attacked Ford. Hannah was remanded to St. Anne's psychiatric hospital, where she told a visiting Cole that she had done everything for him. Hannah tried to get Ford to report Eli to the police, but he told her Eli threatened to kill him if he said anything. Ford told Hannah to write everything down in a letter that would be given to authorities if anything happened to her, saying he had done the same thing. But Eli intercepted Hannah's letter before she could send it off.

Eli forced Hannah to take a bottle of pills, threatening to kill Cole if she didn't comply. Hannah would have died, but Cole found her unconscious and got her medical attention. Everyone soon learned that Eli was behind everything, and Hannah explained that Eli threatened to kill Cole if she didn't go along with his plan. Hannah was humbled when Marty thanked her for saving her son's life and offered to help her recover. Hannah admitted to Marty that she became obsessed with Cole, and Ford before him, because she felt estranged from her parents. Hannah's parents paid for her medical care but didn't bother to call or visit Hannah, and Hannah told Marty that her parents viewed her as a disappointment. Marty testified on Hannah's behalf when she faced charges for obstructing justice, and the judge agreed to release Hannah into Marty's care. Hannah moved into Marty's home, where she overheard Marty warn Cole not to get too close to her because it could take her a long time to get over her obsessive tendencies.

Hannah seemed to be getting her life back on track, and she was genuinely surprised when Cole showed up one day and said he was tired of pretending there was nothing between them. Starr wasn't staying away from James, so Cole said he shouldn't stay away from Hannah. Cole drew Hannah into a passionate kiss, but Hannah pulled away and said she worried that Cole would never leave Starr for her. When Cole learned that Eli was on the loose, he decided to stay with Hannah instead of going home to Starr and Hope. Then John showed up and told Cole that Starr and Hope had been kidnapped by Eli, along with Dani. Cole quickly left to try to find Starr and Hope, leaving Hannah alone at Marty's house. Cole unknowingly left behind his cell phone, and when Starr called Hannah answered. Starr told Hannah she had broken free of Eli and was in a room at the Cherryvale Clinic and told Hannah to send Cole after them. But Hannah appeared instead, telling Starr that Cole wasn't coming. Hannah hit Starr over the head and then locked Starr and Hope inside the attic of her parents' house.

Hannah revealed to Starr that she hoped to be with Cole permanently once Starr and Hope were out of the picture. Starr made several attempts to leave, but Hannah threatened to shoot Starr and Hope. Hannah threw Starr's relationship with James in her face, even ripping James' bullet necklace off of Starr's neck. When James later found Hannah with the necklace, Hannah lied that Cole had taken it from Starr and thrown it away. Hannah worried that James was suspicious of her, and she decided to step up her plan. When James confronted Hannah about her involvement in Starr and Hope's disappearance, Hannah came clean to James before pulling out a gun and forcing him into the same attic where she was keeping Starr and Hope. Hannah then forced Starr and James to dress up in Halloween costumes and dig their own graves at a graveyard while Hannah watched over Hope, telling the baby that she would soon be her mother. When James tried to grab Hannah's gun, Hannah knocked him out and pushed him into the open grave and forced Starr to cover him with dirt.

Just as Hannah was about to shoot Starr, James reached out from beneath the ground and grabbed Hannah's leg. Hannah fell to the ground, and Starr hit her over the head with a shovel. The police arrived and arrested Hannah. At the police station, Hannah pleaded with Marty to help her avoid prosecution and help her get well. But Marty told Hannah there was no hope she could be cured, and the police took her away.

Hannah was taken to St. Anne's for evaluation and eventually transferred to Statesville Prison. On New Year's Eve 2011, Hannah escaped during a major prison breakout. She showed up at LaBoulaie and took young Sam Manning hostage at gunpoint. Todd appeared and tried to convince Hannah to let Sam go, but Hannah wanted to find Cole. Just then, Cole appeared along with Starr and James. Cole tried to convince her that he wanted to be with her, but Hannah knew that his heart still belonged to Starr. Hannah aimed her gun at Starr and fired, but Cole was struck instead. An upset Hannah explained she was aiming for Starr, who smacked her across the face. After Cole was taken to the hospital, Todd held Hannah at gunpoint until the police could arrive. Todd told Hannah that he would have no problem shooting her, explaining that he had shot and killed his own mother. Hannah replied that the shooting didn't count since it was in self-defense. Todd toyed with telling Hannah that he had murdered his own brother, Victor Lord Jr., when the cops arrived to take her away. Hannah screamed that Todd was a murderer who was about to confess to her, but the police paid her no attention as they escorted her out the door.