A dysfunctional family faces the wrath of the Slender man, a tall, faceless entity that abducts neglected children and brings them to his mansion in the woods.
The film begins with three student filmmakers, Jay, Alex, and Amy walking through the woods at night filming a documentary about a tall, faceless creature called the Slender man. During the walk, Jay notices a page nailed on a tree that reads 'Help Me'. Alex tells to viewer that the pages were left behind by victims of Slender man before they died. Then they find another page that reads 'Can't Run' and another that reads 'Follows'. Along the way, something goes horribly wrong. Alex's leg is grabbed by some black tentacle and it dragged him away leaving Jay and Amy in fright. They find another page that reads 'Always Watches No Eyes' and then Jay gets dragged away leaving the camera on the ground until, a terrified Amy picks it up and apologies to her family knowing that she's next. Then she finds another page that reads 'Don't Look Or It Takes You'. Static starts picking up and Amy hears an intimidating voice saying her name. Ignoring the note, she turns around and see's the Slender man. She screams before it attacked her and the camera shuts off.
The next scene takes place in a suburban neighborhood where the dysfunctional Rogers family live. Eric, his wife, Julia, their two daughters, 16 year old Alexis and 5 year old Sally, and their strange grandmother, Doris. After her husband died, Doris asked her son, Eric if she can move in with the family because she doesn't like living alone and ever since she moved in, she hanged Crucifix's in every room of the house. Every time her grandkids asks her why she's being so odd, she replies that its for their own good. That night, Alexis heard her little sister, Sally laughing in her room. Why she walked in, she see's her playing catch with her 'imaginary friend' named Slendy. She shows Alexis some drawings of her friend and Alexis asks why he has no face. Sally replies that he doesn't need face to see, hear or talk.
While Doris was sleeping, she started hearing intimidating voices in her head saying that it will take her grandchildren. The next night, Alexis goes to her friends house for a slumber party. Claire was talking about those three filmmakers that disappeared and says that it might be because of the Slender man, a faceless entity that abducts children at night, takes them to his mansion in the woods, and devours them. But thinks that he might be a bedtime story and that the kids were probably mauled by a bear. When Alexis goes into the bathroom to brush her teeth, the girls hear her screaming so they ran to the bathroom, and they find Alexis missing. On the next day, police start a search party to find Alexis. Doris hears the Slender man voice in her head again. Saying that Mason is next. So she tells her family that Alexis was taken by Slender man and that he's going to take Mason and then Abigail. Eric asks his mother how she knows the Slender man, and she explains that she is a witness of the demon.
When she was a little girl, she went hiking with her parents until he chased a butterfly and got lost in the woods, The Slender man then dragged her to his mansion and locked her in the basement. Eventually, he was going to eat her but, she managed to escape, and then her parents found her. But the Slender man continued to haunt her to this day, and as a result, she went crazy and became obsessed with protecting herself and her family from him. So they locked all the doors and boarded all the windows hoping that would be safe. Little did they know that Slender man has teleportation powers. That night, while everybody was asleep, Eric and Julia woke up hearing Sally screaming as they were being dragged away by the Slender man. So Eric, Julia and Doris head out through the dark woods to find Slender man's mansion and get their kids back. When hope seemed lost, ghost children (who were victims of Slender man) appeared and guided them to his mansion. They find Alexis, and Abby standing by the front door, brainwashed. Slender man grows a mouth and prepares to eat the kids. Until Doris tells him to let them go and to take her instead. Slender accepts her request. He grabs her with his tentacle, drags her into his mansion and presumably eats her. The kids, now back to their normal state, reunite with their parents and mourn the loss of the grandmother who sacrificed herself for her grandchildren.
In a post-credits scene, Slender man targets his next victims.
Lin Shaye as Doris Rogers
Patrick Wilson as Eric Rogers
Rose Byrne as Julia Rogers
Mackenzie Foy as Alexis Rogers
Maya Le Clark as Sally Rogers
Ralph Fiennes as Slender man
Jeremy Irons as Slender man (voice)
Main article: Slender: The Arrival
The production of a sequel was announced.