Logan Brandt, later Laurie Colson, is the central hidden antagonist of Absentia, Season 1, portrayed by Lydia Leonard. Logan was one of the orphans at the same orphanage as Emily Byrne, picked to partake in Dr. Shen's trials of torturing kids into being soldiers.
Emily was meant to be the candidate, but she switched her profile with Logan's, avoiding the torture and continuing to wait for adoption. After six years of experiments, once she grew up, Logan reinvented herself as Laurie Colson, finding Conrad Harlow as an accomplice for her revenge scheme. The two became a duo of serial killers, targeting young women as their victims, for the purpose of later framing Emily for those murders.
Shen was her first victim, which was more for revenge than for making Emily look bad. They - Charles, also known as ‘Subject A’ in the experiments - stabbed him, as well as had a crude signature of cutting his eyelids off, just like the rest of her victims. All of them were found later in season 1, buried on grounds near their bunker in the woods. Harlow and Laurie then kidnapped Emily and subjected her to six years of torture by Shen's experiments as well, with their own modifications. As a distraction, Harlow took the fall for her "murder", only to lead Emily to be found six years later. Logan/Laurie hoping she'd end up a traumatized success even better than Logan/Laurie did. Laurie, getting a job as a journalist, made veiled provocations at Emily to worsen her mental instability and homicidal conditioning, all the while pretending to "help" the investigation with Emily's colleagues and allies, while Emily was spinning more and more out of control as she fell further down the rabbit hole. It came to a head when Emily's son, Flynn Durand, and his stepmother, Alice Durand, were kidnapped and held captive in the bunker. Eventually, Emily, now the prime suspect in the crimes, was taken as well when she infiltrated the bunker. By a now revealed Logan/Laurie, she was nearly goaded into killing Alice so Flynn wouldn't be murdered, but eventually, with the help of Nick Durand, her ex-husband, they all escaped, and after a lengthy shootout and Emily being stabbed, she caught Logan/Laurie, who was drowned in the woods' water until dead. The woods were investigated, and then they eventually confirmed that the bodies previously dug up by Emily were all the victims of Harlow and Colson.