Abbie is called to the station to help with the interrogation of a suspect. Irving introduces Abbie to Dr. Mara Vega, a forensic psychologist who helped them with the arrest, and then tells Abbie that Ichabod is interrogating the female subject. Abbie watches as Ichabod browbeats the girl, demanding to know what she sees. He finally addresses her by name--Abbie-- and Abbie realizes that it's her teenage self. She storms into the interrogation room and the door slams shut behind her and locks. Ichabod, his eyes a solid white, tells her to stop lying and that the truth will set her free. The young Abbie is gone and Abbie turns to try and get out. As she pounds on the mirror, yelling at Irving to let her out. A bone-white figure with dark hollows for eyes appears behind her and advances forward...
... and Abbie wakes up from her nightmare. She gets a call to downtown and drives there, and finds Ichabod waiting for her. Abbie tells him that she had a dream but is interrupted when Irving comes over and tells them that Dr. Mara Vega is up on a window ledge and threatening to jump. The doctor insists on only talking to Abbie and the lieutenant goes up to talk with her. Vega tells Abbie that everything "she" saw was real, but Vega and the others lied about it. The psychologist says that it's her fault for lying and tells Abbie that the girl she lied about was Jenny Mills. When Vega turns to face Abbie full-on, Abbie realizes that the woman's eyes are a solid white. The psychologist says that they all have it coming and then jumps to her death.
When she goes back down, Abbie tells Ichabod and Irving what happened. They examine Vega's corpse and discover that her eyes are white, just as Abbie described. As they stare in surprise, the eyes dissolve into white sand. Abbie figures that Vega must know Jenny and Irving asks her if Jenny ever stayed at Tarrytown Psychiatric. When Abbie confirms that her sister did, Irving explains that Vega worked there several years ago. Once Irving leaves, Abbie tells Ichabod about her dream and he suggest that it was prophetic dream given to her because she is one of the Witnesses, sworn to fight against the coming Apocalypse. While Ichabod admits that he doesn't know what specific creature Abbie saw in her dream, he figures that it's one of the army of evil that
As the sun comes up, Abbie tells Irving and Ichabod what they saw. They check Vega's corpse and discover that she has massive cataracts. As they examine Vega's eyes, one of them pops with a small explosion of sand. Abbie figures that since Vega mentioned Jenny, she knows her sister. Irving confirms that Jenny stayed at Tarrytown Psychiatric and that Vega worked there. After the captain leaves, Abbie describes her nightmare to Ichabod. He believes that she had a prophetic dream because Abbie is one of the Witnesses, and suggests that the pale creature she saw in her nightmare was a member of the army of evil that his wife warned him about.
At the archive, Abbie plays a tape of one of Vega's interviews with Jenny. Going over Vega's case files, they realize that Vega accepted Jenny's story of a demon as truth, but let her institutionalized anyway rather than risk the slur on her reputation for believing a patient's delusions. Abbie figures that Vega killed herself out of guilt, but Ichabod insists that there's more to it given the sand-filled eyes and the dream. He figures that Jenny is a threat to their enemy, the Demon, and that they must speak to her. Abbie doesn't want to talk to her sister, clearly uncomfortable with the idea, but Ichabod insists and Abbie reluctantly agrees to meet with Jenny.
As they go into the institution, Abbie warns Ichabod that Jenny is a criminal and won't help her. She tells her friend that Jenny was arrested after she broke into a sporting goods store and stole $4,000 worth of survival gear. They locked her up in an institution after she claimed that she was preparing for the End of Days. The front desk nurse tells Abbie that Jenny is in Room 49, and she remembers the vision of Corbin telling her about 49. Ichabod wonders when Abbie last saw her sister and she admits that it was five years ago at her arraignment, but Jenny refused her help.
After checking with Jenny, the nurse informs them that she won't talk to Abbie. Abbie is glad to leave, but Ichabod suggests that he talk to Jenny alone. When Abbie agrees, Jenny lets him in out of curiosity. She's impressed with her visitor in spite of herself and Ichabod assures her that he knows she's not insane because he's seen the Demon as well. Jenny tells him not to talk too loudly about demons in an institution, and mockingly says that Abbie is free because she wouldn't talk about them. Ichabod tells Jenny that Vega is dead and she said that she and others had it coming. When he tells her about the Four Horsemen and how Death is at large, Jenny says that there's nothing she can do to help. She tells Ichabod that her conscience is clear and suggests that Ichabod ask Abbie if she can say the same.
As they leave, Ichabod wonders what is going on between Abbie and her sister, and says that they need to face the truth to understand what they're up against. Abbie finally explains that after she and Jenny saw the Demon and the four white trees, they blacked out for four days. The whole town turned out to search for them and a rancher, Garrett Gillespie, found them first. As he approached them, he saw the Demon moving in the woods. However, he never spoke up about what he saw. The police interrogated the two sisters and Jenny said that she saw a demon. However, Abbie refused to say anything about what she saw and they institutionalized Jenny, assuming that she was insane. Abbie kept silent because she and her sister were in a good foster home and she was afraid that they would be put back into the system if they told the truth. Ichabod assures Abbie that she doesn't have to be afraid anymore, but Abbie insists that whatever happened is just between her and Jenny. Ichabod suggests that they talk to Gillespie and see if he will finally confirm what Abbie and Jenny saw.
Gillespie is out in his workshop and dozes off. He hear something and jerks awake, and assumes that it's his wife Paige. He goes into the next room but there's no sign of her, and he scratches his leg on a nail. When he wipes the blood off on a rag, it forms an odd Indian symbol. Something moves around the garage and Gillespie takes out his pistol. The white-skinned figure appears behind him and Gillespie spins and fires.
At the station, Irving discovers that someone has left the decapitated horse sign in his office. He goes out into the squad room and demands to know who left it there. Luke sheepishly admits that he did it and that it's tradition to prank the new guy. Irving glares at him for a moment and then tells him that it's a good joke. He comments about how Luke used to date Abbie, and Luke is surprised that Irving knows about his past. Before he can pursue the matter, they get a call about a shooting out at the Gillespie ranch.
Abbie and Irving arrive at the ranch and are surprised to discover Irving there. He explains that Gillespie has taken his wife Paige as a hostage and will only talk to Abbie. She agrees to go in and finds that Gillespie has broken a mirror and a framed photo of he and his wife. Abbie goes into the kitchen and finds Paige cowering in a corner. Gillespie is seated on the floor nearby, his eyes solid white. He tells Abbie that she can't help him and then fires in Abbie's direction when he sees the white figure standing behind her.
When they hear the gunshot, Irving mobilizes his men. Ichabod runs toward the house while Abbie calls Irving on the radio headset and tells him that everything is fine. She sees Ichabod outside on the lawn and waves him back, and tells Gillespie that she can help him. The rancher tells her that the Sandman is coming for her and that it will kill her the next time she sleeps. Pushed to the brink of madness, Gillespie then shoots himself in the head with his own gun.
Afterward, Ichabod finds Abbie standing by herself and tells her that it wasn't her fault. She points out that Vega and Gillespie could have helped Jenny but didn't, and that she did the same thing... and the Sandman will make her pay the same way. Abbie describes the modern-day Sandman from fairy tales and they figure that the Sandman is the pale-white creature from her nightmare. They go back to the police archive room and find references to dream spirits. Some of them are hostile and one of them is represented by a symbol that Ichabod recognizes. He tells Abbie that it's the Ro'kenhrontyes, a spirit that matches the description of the creature in her dreams. When Ichabod fought with the Mohawk tribes during the Revolutionary War, they told him of the creature and how it killed those who ignored the plight of others. The symbol was a token that warned off the creature, but it had no real power over the Ro'kenhrontyes. Ichabod suggests that they talk to a Mohawk shaman, and is shocked when Abbie says that most of the tribes were wiped out by the white man. The lieutenant remembers that there's one modern-day Mohawk that might know something, but warns that he's not what Ichabod is expecting.
Abbie takes Ichabod to the shaman: Seamus Duncan, a used-car salesman. He greets them but when Ichabod mentions the Ro'kenhrontyes, assumes that they're joking. Ichabod explains that the demon is stalking Abbie, but Seamus doesn't want to hear it. He tries to walk off, but Ichabod warns him that the Ro'kenhrontyes will come for him if he ignores Abbie's plight. Seamus reluctantly agrees to help and drives them to a lodge he has in the woods. When they arrive, Seamus tells them that Ro'kenhrontyes forces its victims to face their guilt until it drives them insane and they kill themselves rather than face the unending pain.
Seamus gives Abbie some special tea to drink that will put her to sleep and allow her to enter Ro'kenhrontyes's dreamscape. However, the demon spirit will choose the challenge she must face, and if she dies in the dream then she dies for real. Rather than let Abbie face the spirit alone, Ichabod grabs the tea and drinks it as well. Seamus warns them that while the tea will put them to sleep and let them find each other in the dreamscape, scorpion venom is required to let them control their actions. He and his assistant strap Ichabod and Abbie down and then force scorpions to sting them.
Abbie finds herself in a forest, and hears Ichabod calling for her from somewhere in the distance. Before she can find him, Ro'kenhrontyes finds her and throws sand into her face. In the Mohawk lodge, Abbie's body convulses and her eyes turn white.
In the dreamscape, Ichabod finds a door in the middle of nowhere, hanging in midair. He opens it and passes through.
Ro'kenhrontyes taunts Abbie, telling her that she has been found wanting. She tries to shoot the creature but the bullets pass harmlessly through it. It transforms into sand and sweeps her away, and Abbie finds herself outside the interrogation room where she and Jenny were questioned about what happened in the forest. Jenny insist that she saw a demon and turns to Abbie for support. The officer conducting the interrogation transforms into Ro'kenhrontyes and looks at Abbie through the one-way mirror, and asks if it saw the demon.
Ichabod passes through the door and finds himself in an old house. Gillespie and Vega are hanging by their necks, dead, and there's a third empty noose waiting for Abbie. Realizing that time is running out, Ichabod continues his search for Abbie.
While the younger Abbie insists that she saw nothing, the adult Abbie echoes her. Ro'kenhrontyes passes through the mirror, reaching for Abbie's eyes. As the creature steps through, Ichabod arrives and tells the demon to step away. It tells Ichabod that his sins aren't for it to punish, and crushes him to the floor with a gesture. When Ichabod tries to fight back, Ro'kenhrontyes cuts off his arm with its razor-sharp talons, transforming the severed limb into sand.
Abbie speaks up for the first time, telling Ro'kenhrontyes to stop. She admits that she lied about seeing the demon to protect herself, and she betrayed her sister. Ro'kenhrontyes tries to advance on her but starts transforming into glass. Abbie tells the demon spirit that she won't abandon her sister and that she's not afraid anymore, and grabs a chair and smashes Ro'kenhrontyes into pieces.
Ichabod and Abbie jerk awake in the lodge, alive and well.
Later at the archive, Abbie wonders how much more they will have to go through given the seven years of tribulations prophesied in the Book of Revelation. Ichabod has nothing to reassure her with, and Abbie tells him that she has to leave to take care of some unfinished business. Irving arrives and asks why they're there, and Abbie explains that they wanted to be close to the police station but out of the way. The captain agrees to let them stay and gives them a key. Ichabod asks if he wants to know what they did, but Irving doesn't need the details as long as they're sure the suicides have stopped. Once he leaves, Abbie can't bring herself to apologize but Ichabod tells her that he understands nonetheless. He suggests that she need to visit her sister and Abbie tells him that was the unfinished business she was going to deal with.
Abbie arrives at the psych hospital and convinces the night nurse to let her in to see her sister. However, when they enter the room, they discover that Jenny is gone. While the nurse goes to lock down the building, Abbie confirms that her sister escaped through the ceiling tiles.