As a young police officer Patrick Mulligan was escorting Frances Barrison to Ravencroft Institute when she unleashed a sonic scream that deafened him in one ear and caused the van to crash. As Frances tried to grab his gun, Mulligan shot her in the face, blinding her in her left eye and believing her dead.
In the present day, at the San Francisco Police Department headquarters, Eddie Brock protested to Detective Mulligan that he wanted nothing to do with Cletus Kasady, Mulligan gruffly saying that the serial killer refused to talk to anyone else - adding that as far as he was concerned Eddie already had his chance with Kasady and blew it. As Eddie asked what Cletus wants, Mulligan theorized that he was finally ready to tell the police where the missign bodies of his victims were buried, admonishing Eddie to do the right thing for a change. As Mulligan walked away, Venom - an alien symbiote bonded to Eddie - manifested its head and attempted to bite his head off, only for Eddie to duck into a nearby bathroom. As Eddie hid in a toilet stall, Venom berates him for stopping it and snarls that they should be out protecting the city by eating bad guys. Hearing the commotion, Mulligan backtracksed and listened against the door. Exiting the bathroom and almost running into Mulligan, Eddie told the police detective he'd do it. Scowling, Mulligan bluntly stated that he didn't like Eddie.
As Eddie exited the San Quentin Prison, Detective Mulligan demanded to know what Eddie got out of Cletus and was infuriated to hear it was only a short poem. Mulligan ordered Eddie to keep him updated the moment Cletus revealed anything of importance, but Eddie frivolously replied that the only scoop he was getting was a double-chocolate chip. Some time later, forensic investigators unearthed the bodies of Cletus' missing victims. Brock's exposé on the discovery reignited his journalistic career, and livid that Eddie published the discovery instead of going to him with the information, Detective Mulligan furiously crumpled a newspaper with Eddie's article on the discovery into a ball before tossing it into a garbage can.
When Casady escaped from his scheduled execution, Eddie heard a knock on the door and opened it to find Detective Mulligan there. Remarking that he was surprised Eddie wasn't dead, Mulligan asked to come in and remarked that the reports coming in from San Quentin were crazy. Eddie asked how Cletus escaped, but Mulligan revealed he suspected Cletus said something to Eddie during their final confrontation that Eddie was withholding. Eddie remarked that he didn't know anything, but Mulligan didn't believe him and demanded to know how Eddie could say that while being at the center of strange events. Worried, Eddie again asked how Cletus escaped, but Mulligan refused to answer as revenge for Eddie not going to him with the information about the missing bodies. Advising Eddie to lay low, Detective Mulligan left to continue hunting for Cletus.
Later, from the now-decrepit St. Estes', Eddie called Mulligan and revealed that Cletus had a romantic partner he was looking to free. Realizing Eddie is talking about Frances, Mulligan told Eddie that he killed her years ago. Mulligan hung up as his deafened ear ringed with tinnitus and he had a flashback to his confrontation with the teenaged Frances. At Ravencroft, Detective Mulligan arrived to find the warden dead and Frances' cell torn apart. Turning to the SWAT trooper accompanying him, Mulligan ordered an APB be put out for Cletus and Frances, state lines be blockaded, and Eddie Brock be brought in for questioning. At the police station's interrogation room, Eddie protested he didn't know anything but Mulligan accused him of lying, suspecting him to be in league with Cletus. When Mulligan mentioned reports of a monster accompanying Cletus, Eddie realizes that Cletus bonded to a piece of the Venom symbiote after biting him. Anne Weying bickersedwith Detective Mulligan before being let in to see Eddie. Detective Mulligan attempted to eavesdrop, but was alerted that St. Estes was burning to the ground. Hearing the noise, Detective Mulligan found a gaping hole in the wall of the room and realized that Eddie tricked him, furiously throwing the chair into a wall.
Detective Mulligan arrived at Eddie's apartment to find Cletus Kasady waiting outside. Drawing his gun, Mulligan orderde Cletus to put his hands on his head, but Cletus mockingly transformed into Carnage. As Mulligan futilely empties his clip into the red symbiote, Carnage growled that Frances would be pleased. Alomg with Anne Weying, Mulligan was brought into the the Grace Cathedral as one of the "presents" for thw wedding of Barton and Casady. Frances crawled over to Detective Mulligan, who was increduous to see her alive, but before she could exact her revenge Carnage grabs her and told her not to use her sonic powers. Taking advange of the distraction, Mulligan crawled into one of the construction elevators and activated it. Arriving at the scaffolding on the outside of the cathedral, Mulligan attempted to radio for backup but as stabbed in the shoulder with a paint shovel by Frances, who pinned him to the scaffolding and declared her intent to gouge out his eye as revenge for him blinding her. Wrapping a chain around Mulligan's neck, Frances gleefully kicked him off the scaffolding in an attempt to lynch him. The fight between the symbiotes ended in Frances falling to her death while Cletus and the Carnage symbiote were both eaten by Venom. In the scaffolding of the church, Detective Mulligan regains consciousness, his eyes turning an eerie blue with black sclerae.