It is 1934 in Arkham, Massachusetts.
Arthur Lester, private investigator, wakes up on the floor his office, blinded and hearing a strange Voice in his head. Next to him, he soon discovers, is the dead body of Peter ‘Parker’ Yang, his partner, as well as a book bearing a strange sigil on the cover. The Voice in Arthur’s head explains that it has taken control of Arthur’s eyes - it can see, but he cannot.
Arthur’s memories gradually begin to return: he remembers that he opened the unfamiliar book and then killed Peter, though he does not understand why. The Voice urges Arthur to conceal Peter’s murder by hiding his body in the office cupboard. In the process, they find packaging for the book with a sender’s address: J. D. Ackerman’s Rare Books.
They are interrupted by Eddie, the building supervisor, who seems suspicious of them. Eddie insists that he be allowed into the office to do maintenance work. After failing to persuade him to come back another time, Arthur threatens him. Eddie leaves, but begrudgingly.
The Voice in Arthur’s head reveals that he was previously imprisoned inside the book and insists they go directly to the shop from which it was sent. Arthur speculates about why the book may have been sent, wondering if it is connected to a recent job he and Peter had taken: a missing persons case during which they visited a house with the sigil from the book’s cover painted on the basement door.
Prompted by Arthur’s questioning, the Voice explains that it comes from the ‘Dark World’, a ‘collective junkyard’ and the ‘ultimate end’ of everything where all the different versions of the world that exist terminate. There, the Voice explains, it was bound to a book, then the book was somehow passed into Arthur’s world. The voice claims to not remember his previous life or who he is.
At the bookshop, the Voice is distracted by a song on the radio, a rendition of You Call it Madness (But I Call It Love), which he seems to recognise. Arthur and the Voice realise there is an intruder and the shop has been ransacked - a man in a white mask emerges from a back room, shoots at them, and flees. Searching, they find no record of the book being sent to Arthur and Peter's office - Arthur suggests that this means it was being concealed on purpose, as it was wrapped to look like any other package and yet was not included in any of the normal records. They also find the shop’s rolodex already open to their address, although it is listed as the office of Roland Cummings, another private investigator and the previous occupant. They decide to continue on to the house where Arthur found the sigil.
They arrive at the house. It is normal-looking, if a little isolated. Arthur recalls that the victim, a young girl called Emily MacFarland, was eventually found dismembered in a field and that her murderer has not been caught. The Voice grows angry, asking if Arthur really tried to solve the case at all. They go down into the basement, but discover a mural of a horrifying creature, which the voice names as Shub Niggurath. There, they find a further passage leading down to a cave far beneath the house, which holds a ritual space, including a sacrificial slab, an empty stone archway, and a podium where the Voice’s book fits. They also find the remains of two people, one of whom has been dismembered the same way Emily MacFarland was. The Voice proposes that whatever creature was summoned by the cultists in the cave was released by Emily, killed her, and might now be roaming free.
Arthur and the Voice discuss the cave and what they have found: Arthur believes the bodies were worshippers of Shub Niggurath, killed in a ritual went wrong, while the voice suggests that the stone arch was used as a gateway and that the cult might have brought him out of the Dark World. Arthur proposes they go to the library at the University of Miskatonic next, to gather information.
Once there, they ask the librarian, Mr. Armitage, for information on Shub Niggurath. He warns them, but allows them to view a private collection. They also check the newspaper records for the area around the house, Pelican Lane, and find an article about a missing girl from nearly ten years ago: Amanda Cummings (apparently the daughter of Roland, the previous occupant of Arthur’s office and another private investigator). According to the article, Amanda was found walking in the area around the house with another girl. Both had been held captive but refused to talk about their experiences to the authorities.
Next, they read the book about Shub Niggurath. It features entries on various bizarre creatures. The Voice finds a prayer in praise of Shub Niggurath and notes added in a later hand describing her as a terrifying creature who buds dangerous entities called 'Dark Young'. The Voice tries reading a description written in a strange language, which distresses Arthur. Arthur proposes they use his connections to access police records, while the Voice argues they should investigate the Cummings family and focus on trying to find Amanda instead.
They try to return to Arthur's office, but find police waiting outside. The Voice insists they go in, despite Arthur’s fervent objections. They gain access to the building via an alleyway and find an address for Cummings, but are attacked by Eddie, the building supervisor. He begins beating Arthur, who does not fight back even as the Voice urges him to kill. Eventually, Arthur reaches for his gun and shoots Eddie, who reels back. Then, Arthur realises that one of his hands is wrapped around the man’s neck, strangling him. The Voice notes, smugly, that it has gained control of one of Arthur’s hands. Eddie dies from the combination of the gunshot wound and the strangulation. As Arthur panics, the Voice insists that killing Eddie was what Arthur wanted and that the voice is after its own body, not Arthur’s.
They head to the Cummings house, but find it abandoned. To the Voice’s frustration, Arthur sits down on the porch and refuses to move, saying he is frustrated and unsure. A neighbour emerges and tells them what happened: Mrs Delphine Cummings was found dead in the house’s freezer, Roland disappeared and is suspected of her murder, and Amanda has moved to the town of Harper’s Hill. The Voice and Arthur decide to drive there to look fo her, but on the journey Arthur grows quiet and reserved - he is concerned that he seems to be losing parts of his body to the voice.
They come across a car abandoned by the side of the road. One of the doors is open, leading into the woods, and there is blood on the seat and signs of a small child having been in the car. They follow the tracks to a small gaggle of huts and, inside one, see a dead body and a terrifying old woman holding a baby. The old woman allows Arthur to take the child easily, merely laughing at him.
They inspect the baby and find that a symbol has been drawn on her before realising they are being followed by some kind of creature. They run back to the car, only to find that the laughing woman from the hut has climbed in with them. In their panic, they crash the car.
Arthur gathers up the baby, and climbs from the wreckage. The Voice urges him to return to the woods and they come across a grand but dilapidated house. The Voice is reluctant, but Arthur insists they go in, as they need shelter for them and the baby. The house is old, run down, and there is a pile of burned items out front. They set the baby down for a few moments, but when they come back she has disappeared.
They begin searching upstairs, where they find an abandoned wheelchair, a bedroom that was boarded up and broken into, and a long-dead woman lying on one of the beds. In the next room they find a ladder to the attic and the body of a dead man. They spot a door leading to another attic room and find a young girl’s bedroom, but are startled by a dead-looking female figure who is sat on the bed, holding the baby and humming.
As Arthur runs, the Voice explains that the woman is a Wraith, a once-human spirit bound to a place. They theorise that the wraith is the dead woman whose body they saw on the bed, that she lost a child in life, and that she has taken the baby as a replacement. However, the Voice explains she will soon kill the baby if they don’t stop her. They must do two things: find something that belonged to her when she was alive and burn her bones, at which point they can either kill her or set her free.
They search the girl’s bedroom and find pictures and a name, "Anna". They progress to the woman’s bedroom, hoping to find an item of hers, but realise that a necklace the dead woman was wearing was removed long after her death - someone has clearly broken into the house before them. Clutched in the dead woman's hand, they find a small portrait of a baby boy, "Eric".
Carrying on down to the basement, they fall through the rotted stairs. Down there, they find a wheel connected by wires to a strange amalgam of a typewriter and a dead crow. Each time the wheel is turned, the typewriter/crow produces: "The Black Goat comes". They check the desk and find a birth certificate for an "Eric Stanczyk". The typewriter starts up again, even though Arthur is not touching the wheel. The Voice identifies a number of deep cuts in the stone walls and a chimney through which they can climb up to escape the basement.
They decide to use the name ‘Stanczyk’ to summon the wraith, take the baby, burn the woman's bones, and bind her to the wheelchair. Arthur rejects the idea that they free the Wraith at first, but the Voice explains that they can do it by offering a deal - they ask her for something that she can accomplish, she fulfils it, then she is let go. Arthur suspects that the Voice wants him to let the Wraith go rather than destroy her, and the Voice explains that he hopes any creature can be redeemed.
The wraith is summoned and places the baby down when Arthur offers her a bundle representing the ‘baby Stanczyk’. Although she realises the trick that has been played on her, it is too late: her bones are burned and she is bound to the wheelchair. The Voice asks what Arthur plans to do now.
Arthur and the Voice decide to head back to town, Arthur in particular hoping to find someone to whom he can give the baby. They approach a diner and see a distraught and injured woman inside who they guess might be the baby’s mother. At the same time, the Voice spots a nearby car marked for Harper's Hill, the town where they believe Amanda Cummings to be living. Arthur suggests they leave the baby on the diner steps and hitchhike.
Arthur asks the Coice to describe the baby: the Voice seems exasperated by this request, but does so. They leave the baby on the step and wait until she is discovered by the woman. They they then got to hitchike, but in his hurry and without his sight, Arthur approaches the wrong car to ask for a ride. The driver inside agrees.
The driver introduces himself as Kellan, and he wears a gas mask due to injuries he claims he sustained during World War I. Arthur soon realises that Kellan is emotionally unstable and very easily angered, especially by any sign that Arthur is trying to leave. Kellan repeatedly references voices in his head that only he can hear. The Voice in Arthur’s head, meanwhile, urges Arthur to escape, but Kellan threatens Arthur if he tries to run.
Kellan drives until they reach a half-built wooden house in the woods where he brings Arthur down into the cellar. Suddenly, Kellan asks Arthur how he managed to get the voice in his head to listen to him. Arthur, intrigued, admits that he does in fact hear a voice, much to said Voice’s frustration. The Voice in Arthur’s head calls Kellan’s mother a whore as a test to see if Kellan really can hear him, but Kellan does not react. Instead, Kellan leaves and the Voice reveals to Arthur there are chains in the cellar - they are going to be held captive.
They realise they need to get Kellan’s car keys, which he carries in his pocket. Leaving the cellar, they find photographs of Kellan with his sister, as well as a rifle. They find and approach Kellan, who is standing at the end of a dock looking over the lake. He tells them that ‘she’ (presumably his sister) heard voices too, but that they were not like his own and that he needs to check on his sister. He begins to pull on a chain, dredging a birdcage containing a decomposing human head up from the lake. He speaks to it briefly, then turns to Arthur, angrily saying that his mother was not a whore - Kellan does not know what the Voice in Arthur’s head says, but the head from the lake apparently does. Kellan becomes distressed when the head tells him that she wants to go with Arthur, threatening to slit Arthur's throat to prevent this. Arthur tries to shoot Kellan, but discovers that the rifle is not loaded.
Arthur and the Voice run and hide, coming up with the plan to distract Kellan and escape by starting a house fire and stealing a boat. Kellan chases them into the house and they succeed in setting his bed alight, but Kellan stabs Arthur in the stomach. The Voice urges Arthur to keep moving, though surprisingly gently, and it is clear that Arthur is bleeding heavily.
They push the boat into the water and Arthur gets on board, but goes back to the dock to get the head, as it offered to help. Kellan attacks again and he and Arthur struggle, but Arthur eventually slashes Kellan's throat. The man's final actions is to detach the chain and remove his gas mask. Arthur takes the cage with the head and begins paddling out onto the lake as fire and smoke pour down to the banks. Arthur begins to faint from blood loss and the Voice apologises: ‘If this is the end… I’m sorry’.
As Arthur’s consciousness fades, there is the sound of a Wraith-like wail and a deep, distorted voice: ‘This too shall pass’.
Arthur wakes to a strange voice - a new one. This new voice is chatty and teasing, identifying itself as Adam Fry. According to Adam, he and Arthur are in cells next to one another in an asylum. The walls are padded, most patients are tied up, and there are regular guard patrols. A "guard" passes by the door, the sounds revealing that it is some sort of creature. Adam says he has an escape plan, but refuses to let Arthur in on it unless he gives him more information regarding what he was doing before waking up in the asylum. Arthur begins to explain that he was searching for a girl called Amanda Cummings, until he realises that Adam keeps calling him Arthur despite him never having told him his name. Adam’s voice immediately shifts to something deeper, thanks Arthur, and instructs him to ‘sleep well’.
Arthur wakes, this time in the Harper’s Hill hospital and with the familiar Voice. He blearily insists that they need to find Amanda Cummings, but the Voice reveals that Arthur has been in a coma for over a month, during which the Voice has been conscious and aware. The Voice has done a bit of introspection and says he is grateful to have found Arthur. What’s more, the Voice reveals they are considered a ‘John Doe’ and that one of the friendlier nurses would talk to them, always referring to them as ‘John’. The Voice decides to adopt the name John.
They try to work out what was happening in Arthur's dream. Arthur insists they need to leave. He struggles out of bed, shaves, dresses, and sets off to search the hospital. As they go, he and John recap what they’ve established so far. Arthur realises that there is probably some information and perhaps an address for Amanda Cummings stored in the hospital records room. They realise they need to steal a set of keys to the room and find someone in the break-room, sleeping with the radio on. They approach and grab their keys, but the radio suddenly blares static and a familiar rendition of 'You Call it Madness (But I Call It Love)' starts up. They flee and the person quickly goes back to sleep.
They find a file on Amanda Cummings, but it is an autopsy request, as she died a few days before Arthur woke up. They realise her body is still in the morgue and head down to the basement to investigate. John reminds Arthur how important it is for them to keep a low-profile. Additionally, John offers his theory as to why he was able to gain control of Arthur’s hand when they killed Eddie, yet could not gain any more while Arthur was in a coma: he believes it is to do with Arthur being pushed to the brink and that each time his sanity is truly tested John gets more control.
They open the body bag, but when Arthur accidentally touches Amanda's skin John experiences sees a brief image of how she died. Arthur theorises that his time in the dream has given them a new form of insight, but John is reluctant, fearing that this new ability will have a cost attached. They touch her again and John recounts what he sees: Amanda in a small bedroom apartment, putting a diary under her mattress and looking nervous. A man with a warm smile arrives and reaches towards her, his long, thin fingers pushing into her neck and face. All the while, the man looks at John and Arthur. John fears they’ve been tricked by this entity, who cannot reach them but wanted to be seen.
They hear a strange noise. Using their new ability has allowed a creature to travel into their world. They hide in an office, but the creature follows them. John struggles to describe the creature, but is convinced they need to stop it or it will continue hunting them. They slide down a laundry chute into the boiler room. John identifies an incinerator and they use Arthur as bait to lure the creature down the chute and into the incinerator before trapping and burning it.
They go through the lost and found and take a few hundred dollars they find concealed in the lining of a hat. Then, they decide to go into the town and arm themselves before heading to Amanda’s house.
