Hudson Valley, New York – 1781
The American revolutionaries are fighting the British and among them is Professor Ichabod Crane. As he checks the hand of the dead British soldiers, a masked Redcoat rides toward him wielding an axe. Ichabod shoots him in the chest, knocking the man off of his mount, but then the Horseman advances on him, seemingly unaffected. He knocks away Ichabod's rifle with his axe and the professor sees a bow-shaped mark branded on his opponent's hand. The Horseman cuts Ichabod across the chest and moves in for the kill, but Ichabod manages to decapitate him. After a moment, Ichabod collapses next to his decapitated opponent.
In an underground cave, Ichabod claws himself up from out of the ground, gasping for breath. He crawls out and checks his chest, and finds no sign of the wound that killed him. Spotting a flight of stone stairs leading upward, Ichabod staggers over to them and climbs up. Sunlight shines down from above and Ichabod emerges into the open air. Ichabod staggers through a forest… and out onto an asphalt road. A semi roars out of the mist, narrowly missing him, and then a passing car crazes him. It goes off the road and the driver gets out, and a confused Ichabod runs off... past a sign saying Sleepy Hollow.
At a diner in Sleepy Hollow, Sheriff August Corbin is having dinner with his deputy, Lt. Abbie Mills. Corbin rips out an article from the local paper about an unsolved homicide and tells Abbie not to worry about it since she's leaving to go to Quantico and join the FBI. The sheriff talks about how there are so many unsolved cases in the area, while Reverend Knapp watches them from a nearby booth. Corbin wonders if she's running away but Abbie ducks the question and heads out. As Corbin follows her out, he nods in greeting to Knapp.
Out at the squad car, Abbie takes a call about horses at the local livery, spooked by wild animals. The two officers drive to the livery stable and Corbin goes up to the stable while Abbie looks for the owner, Jimmy Ogleby, at the house. Abbie knocks at the door but gets no answer. She looks around and sees Jimmy's truck parked nearby, the door open. Meanwhile, the sheriff goes into the stable and tries to calm the horses down.
Abbie checks out the truck and discovers that it's empty. A rifle is lying on the ground next to it and Abbie calls Corbin on the radio to tell him. She spots Ogleby's decapitated corpse nearby and warns Corbin over the radio. Meanwhile, a headless figure in a British redcoat's uniform advances on Corbin. He shoots at it but the bullets have no effect. It advances on Corbin and decapitates him with its axe, driving the blade through the door behind the sheriff just as Abbie arrives. A few seconds later the Horseman bursts out through the stable doors, riding a white stallion. In the lightning from the storm, Abbie catches a glimpse of a bow-like shape branded on its hand. She turns to the barn and finds Corbin's decapitated body lying on the floor.
Abbie calls for backup, reporting an officer down, and Deputy Andy Brooks takes the calls. He drives to the livery stable but brakes to a halt when Ichabod runs out in front of him. Brooks gets out and orders Ichabod to surrender, and Ichabod does so. Once Ichabod is put in a cell, Abbie checks on him. She tells Brooks that it wasn't the man that she saw kill Corbin. She describes the brand and Ichabod recognizes it, and asks if the killer carried a broad axe. He describes the brand and Abbie wonders how he knows, and Ichabod tells her that he cut off the killer's head.
The next day, the police call in a polygrapher to question Ichabod. The polygrapher informs him that he's being held for Corbin's murder, and advises Ichabod that the best chance for clearing his name is to consent to the test. Intrigued by the machinery, Ichabod agrees and identifies himself as Ichabod Crane, a professor at Merton College sent to fight against the American colonists. However, he witnessed their bravery and had a change of heart, switching sides and spying for George Washington. The polygrapher assumes that Ichabod is insane and asks him about the Horseman. Ichabod goes on to explain that he shot the Horseman and then decapitated him when the Horseman rose back up. As Abbie and the police chief, Captain John Irving, watch from behind a one-way mirror, Ichabod explains that after he decapitated the Horseman, he was taken to triage for his wound. His wife Katrina, a civilian nurse, was there. Ichabod passed out and the next thing he knew, he was in the cave. Ichabod demands answers to his questions, and the polygrapher tells him that he won the war... 250 years ago.
Once he leaves the room, the polygrapher tells Abbie and Irving that the machine indicates that Ichabod believes he's telling the truth. Irving sends him to a mental hospital, St. Gregory's for a psych evaluation. Abbie approaches Irving and asks for permission to interrogate Ichabod. She points out that he described the killer and notes one discrepancy: Corbin's neck wound was cauterized. There were no traces of fire near the area and Abbie figures that Ichabod saw something that can help them find the killer. Irving figures that Ichabod may be the killer and refuses to let Abbie interrogate their prime suspect. She persists, asking if she can transfer Ichabod to St. Gregory's and question him en route, giving her some closure. Irving takes pity on her and grants her request.
Abbie goes to collect Ichabod, who is surprised that she is a black female police officer. He assures her that he was in favor of the Abolitionist Act and asks when he'll be freed. She takes him out to the car and he figures that she's helping him because she's out of options. Ichabod assures her that he believes that she saw a headless Horseman, and figures that it's no coincidence that he arrived there at the same time. Tired of his ranting, Abbie orders him into the car and Ichabod nervously gets in.
As they drive to the institution, Ichabod plays with the window switch until Abbie shuts it off. She then tells him to take her to the cave where he woke up. Ichabod points out that she's disobeying orders but Abbie figures that even if he tells anyone, they won't believe him. They drive by the church and Ichabod sees Reverend Knapp out front. As he sees Knapp's face, Ichabod vaguely remembers the man at his bedside... 250 years ago.
Ichabod leads Abbie to the cave and he finds an old Bible lying on the ground. As he holds it, Ichabod remembers Knapp placing it on his chest when he lay dying. There's a passage in the Book of Revelation marked, foretelling one of the Four Horsemen. In the passage, the Horseman Death is riding a white horse and holding a bow. Ichabod explains that the Redcoats ambushed them in the Hudson Valley. Washington told Ichabod that the outcome of the Revolutionary War would determine the fate of everyone on Earth. The general assigned Ichabod to kill the Horseman, an unknown mercenary with the brand of a bow on his hand. Abbie doesn't accept that the man she's after is one of the Four Horsemen of the Apocalypse, but Ichabod warns that what they're facing isn't a man, and the Horseman has returned to Sleepy Hollow to finish what it started.
The Horseman rides through the forest, its steed's eyes glowing red.
That night, Knapp leaves his church carrying a shovel and goes out to the cemetery. He hears a horse approaching and runs toward the street. The Horseman is waiting, and dismounts and approaches Knapp. Knapp casts a spell, animating the nearby chains and restraining the Horseman, but the figures cuts himself free with his broad axe. It advances on Knapp, who vows to never tell it where it is, and decapitates him.
When Abbie hears about the murder, she drives to the church and tells Ichabod to stay in the car. She locks him in and approaches Irving, while a bird lands on the trunk of her car. It studies Ichabod intently for a moment and then flies off. Meanwhile, Abbie confirms that the wound was cauterized, just like Corbin's. Ichabod manages to get out of the squad car and Irving demands an explanation. Abbie explains that Ichabod was in her custody when Knapp was killed, meaning he can't be the murderer. Irving tells her to get Ichabod locked up or she's suspended. Once Irving walks away, Brooks advises Abbie to follow the captain's orders.
Ichabod follows the bird out to a gravestone in the cemetery and Abbie catches up to him. He checks the stone and discovers that it belongs to his wife Katrina, who was burned for witchcraft in 1782. Ichabod insists that the gravestone proves the rest of his story is true, but Abbie still doesn't believe it. She warns that Irving can stop her from leaving Sleepy Hollow, and Ichabod insists that her fate is intertwined with his. Abbie walks off, saying that she refuses to refuses to deal with something she can't explain, and Ichabod picks up on the fact that something unexplainable has happened to her before. The lieutenant refuses to explain and says that they both need some sleep.
Abbie takes Ichabod to St. Gregory and gets him his own cell. He admits that he has doubts about his own sanity, and Abbie tells him that in high school, she and her sister Jenny were walking home one night through the forest. They saw four white trees together and sensed that something was wrong with them. Something started to emerge from them, and they blacked out. Everyone said they were crazy, and Jenny accepted that. However, the encounter drove her to the brink of insanity and she's been in and out of institutes ever since. Abbie assures Ichabod that she knows what it's like to doubt one's sanity. As she leaves, Ichabod says that she's sorry about her partner's death.
The next morning, Abbie sneaks into Corbin's office and looks at the photos he had of her. She finds a key on the back of one of the frames and finally confirms that it opens a file cabinet. A tape player is inside with notes that Corbin made about the execution of witches in Sleepy Hollow. There were two covens, and some changed their lives and hid among the general populace, while others moved to other cities up and down the east coast. One coven represents good and the other evil. There are hundreds of unsolved murders and disappearances, all of which were ignored, and Corbin could never figure out how they were connected. Corbin has a file on Abbie and Jenny, and how their encounter was similar to one that a farmer had in 1882 on the same spot. The farmer believed the four trees represented the Four Horseman, and the demon was sent to raise them. Corbin didn't know who to trust, and could never figure out how to tell Abbie what he discovered.
Irving comes in and Abbie quickly closes the cabinet and hides the key. He tells her to let him do their job and get some rest. Once she leaves, Irving glances around Corbin's office.
Ichabod wakes up and discovers that the same bird is perched at the end of his bed. It flies through the mirror and out into a forest, where Katrina is standing. She explains that she could only reach Ichabod through his dreams. Katrina was never buried in the grave: it hides the Horseman's skull and was guarded by Knapp. When Ichabod decapitated the Horseman, their blood merged and they became linked. Katrina's cult tossed the Horseman into the river, sealed in an iron box. They then buried Ichabod in the cave to protect him. The evil that trapped Katrina woke the Horseman, and inadvertently woke Ichabod as well through the link.
Something moves in the forest and Katrina warns that it's coming for her. She tells Ichabod that if the Horseman is reunited with his skull then he will become whole, and the other Three Horsemen will follow... and bring about the end. Katrina tells Ichabod that the Horseman can't survive the sunrise and begs her husband to find and free her, calling him the First Witness. As the demon emerges from the forest, Katrina tells Ichabod that the answers are in Washington's Bible and tells him to wake up.
Ichabod wake up in a panic and the orderlies restrain him while a doctor starts to give him a sedative. Abbie arrives and tells the doctor that she's taking Ichabod back into custody. She gives the doctor a court order and quickly gets Ichabod out, and warns that the order was fake. Ichabod tells Abbie that he knows what the Horseman is after. Out in the car, Abbie shows Ichabod a map that Corbin had of the Hudson Valley in 1776. Ichabod remembers that Washington had the map. Corbin marked sites around town, trying to solve the puzzle of what was going on. When Abbie wonders if the trees and the demon were real, Ichabod assures her that he saw it as well and she wasn't imagining things.
At the river, the Horseman emerges from the waters and goes to its horse.
Abbie calls Brooks and asks him to get all units to the church. Brooks is skeptical and warns that if she's wrong then they're both in trouble. He reluctantly agrees to call it in and meet Abbie at the church. When he gets to his apartment, Brooks discovers that someone broke in. He draws his gun and goes in, and finds the Horseman waiting for him, armed with Brooks' stash of guns. After a moment, Brooks tells the Horseman that he knows where its skull is
Ichabod and Abbie get to the cemetery and dig up the grave. They remove the skull, sealed in a jar, As its eyes glow, the Horseman rides into the cemetery and opens fire on them. Abbie runs off while Ichabod takes cover in the grave. Abbie takes cover behind the barrier wall and shoots the Horseman repeatedly when it prepares to kill Ichabod. The bullets stagger it long enough for Ichabod to grab a shovel and attack it. Meanwhile, Brooks pulls up and Abbie tells him to get her a rifle from the trunk of his car. When her back is turned, Brooks pistol-whips her unconscious. He drags her into the back of the car, insisting that he's going to protect her.
When his attack proves useless, Ichabod grabs the jar with the head and runs to the church. Meanwhile, Abbie wakes up enough to bite Brooks' hand. He screams in pain and she grabs his gun and aims it at him. Abbie orders him to handcuff himself to the car door while Ichabod calls for help. Two officers arrive and order the Horseman to surrender, and then stare in shock as they get a good look at it. Before it can respond, the sun comes up and the Horseman starts to smoke. It fires on the officers, forcing them to take cover, and then rides off. Abbie arrives and when Ichabod calls to her, the officer instinctively fire before she stops them.
Back at the station, Irving informs Abbie and Ichabod that they now have evidence to corroborate her story, and Brooks has agreed to plea bargain as long as he can talk to Abbie and Ichabod. When he asks for more info, Abbie warns him that they've only scratched the surface. When Irving asks if she's still transferring to Quantico, Abbie tells him that she now believes that she's supposed to stay in Sleepy Hollow.
As Abbie and Ichabod go to the interrogation room, Ichabod tells Abbie that in his dream, Katrina called him the First Witness. The Book of Revelation speaks of two witnesses, brought together for a seven-year period of tribulation to defend humanity from the forces of Hell. The battle will determine the fate of the world on Judgment Day. Ichabod figures that the two of them are the Witnesses and that she's been called to finish the work that Corbin started.
Brooks is in his cell when the demon enters and tells him that he failed. The officer begs for another chance but the demon kills him with a gesture, breaking his neck. Ichabod and Abbie come in second later and find Brooks' corpse. Abbie sees the demon in the mirror, walking away through the forest. It turns to glance back at them and the mirror shatters.