Sue Ann Ellington's backstory was revealed throughout the film; she was a shy and unpopular student in high school, and she harbored a crush on Ben Hawkins. One day at school, Sue Ann followed Ben to a hall closet, where she and Ben appeared to engaged in a sexual encounter. However, when Sue Ann left the closet, she was shocked to see Ben standing outside and smirking, along with a large group of students--including Erica Thompson and Mercedes. In addition, Sue Ann's act was revealed to be with a different boy, part of an elaborate prank pulled by Ben, who led the students in laughing at her, causing Sue Ann to run off in embarrassment.
In the years that passed, Sue Ann entered a failed marriage which resulted in the birth of her only daughter, Genie, and had worked as a veterinary technician. Her first appearance in the film saw her being encountered by main protagonist Maggie Thompson, who was attempting to coerce passing adults to buy alcohol for her and her four friends, Andy Hawkins, Haley, Chaz, and Darrell, for a party. Sue Ann does so, but notices that the van that they were in had the logo for Ben Hawkins' security company. Afterwards, Sue Ann anonymously reported their activities to the police, and she looked in the group's social media history and learned that Andy was Ben's son, and that Maggie was Erica's daughter. With her new knowledge, Sue Ann began befriending the teens, doing so as part of her twisted revenge plot for Ben's prank, which remained fresh in her memory.
The following day saw Sue Ann invite the quintet to drink and party in her basement, while giving them a set of house rules--the main one being not to go upstairs. Sue Ann basked in her popularity, though her clingy personality began to surface after lashing out at Maggie and Haley for going upstairs during a party, which included sending numerous texts to Maggie and Haley and displaying bitterness when the group turned down her latest invite. Sue Anne managed to regain the teens' trust, however, when she claimed her behavior was a result of her being diagnosed with pancreatic cancer and having to take several medications for it. Later on, however, Maggie and Haley began to suspect that Sue Ann was stealing their jewelry, leading to the pair heading to Sue Ann's home to investigate. It was at the house that the pair encoutered Genie, who was standing despite being shown in a wheelchair in the film's opening with Maggie. The pair hid after Sue Ann's arrival, and it was later on that she was shown drugging Genie and turning down her requests to return to school, with the deranged villainess claiming that she was keeping Genie safe.
Sue Ann encountered Ben and ended up going on a dinner date with him, where Ben revealed that he had a tracking device in Andy's van, after which Ben warns her to stay away from Andy, while also referring to Sue Ann as a loser. Her increasing instability over being ignored by Maggie and the rest of the group led her to conveniently visit Erica at her home, and afterwards, Sue Ann spotted Mercedes (Ben's current girlfriend) jogging and ran her down in her van, killing her instantly. By this point, Maggie had learned about Sue Ann's history with her mother and Ben, and later on, the deranged Sue Ann drew blood from Maggie's dog, Louie, before taking the tracking device from Andy's van as part of her plan to lure Ben to her home, where she drugs Ben before tying him to her bed.
The psychotic madwoman briefly threatened to castrate Ben before lashing out at her former crush over his humiliating prank from high school, while also telling Ben that he is a dog and she will treat him like one. It was quickly revealed that Sue Ann was injecting Louie's blood into Ben, after which she killed Ben by slitting his wrists. A later scene revealed that Sue Ann had also killed her boss, Dr. Brooks. It was after Louie's injury at the hands of Sue Anne that Maggie confessed to her involvement with Sue Anne to her mother, with Erica confronting Sue Anne about her actions when she ran into her at a store and threatening to report her to the police if she didn't stay away from Maggie. In response, Sue Anne boasted about her newfound popularity with the teens and cryptically blasted Erica for her past actions in high school, even muttering as she walked away that she'd "taken care of" Mercedes for her.
Climax & DeathEdit
The film's climax saw Maggie receive a phone message from Sue Ann that showed another party at her place, with the villainess revealing that she had Maggie's earrings. Despite being grounded by Erica, Maggie left her home and went to rescue her friends, only to find that they had been drugged by the evil Sue Ann, who appeared and drugged Maggie after she found Ben's body, later placing a choke collar around her neck along with her other incapacitated victims. Afterwards, Sue Ann ranted about her newfound popularity and subjected her victims to more torment, which included burning Chaz's abs with an iron, sewing Haley's lips shut, and putting white paint over Darrell's face. Regarding Andy, Sue Ann caressed him and told him how much he reminded him of Ben, after which Andy attempted to appease the villainess by kissing her and stating that he loved her. In response, however, Sue Ann stabbed Andy (non-fatally) in the stomach, and then ordered Maggie to take a photo of her with her captive victims.
Sue Ann was interrupted by the appearance of Officer Grainger, who was investigating the garbage from her house. After hearing Maggie's screams, Granger returned to the house, where he was shot to death by Sue Ann, who later lashed out at Genie for opening the door for him and forced her to bring in Granger's body. Sue Ann later returned to the basement and attempted to kill Maggie, only for Genie to stop her crazed mother by knocking her out with a frying pan before releasing Maggie and helping her free her friends. During the melee, a fire inadvertently starts and spreads all over the house, and it was at this point that Erica (along with her co-worker, Stu) arrived and helped rescue her daughter and the others. Sue Ann lashed out at Erica for not doing anything to prevent her humiliation, with Erica expressing her guilt and saying that she should have done something.
All the while, the psychotic villainess held Genie captive and attempted to throw her into the fire, only for Maggie to grab the knife and stab Sue Ann before successfully rescuing Genie. After her victims all escaped, Sue Ann walked to the bedroom and laid next to Ben's body, as the flames consumed the house and eventually killed her.