The Gallows movie explanation (Spoiler Alert)

The movie begins in 1993 where people are watching a play at the school's theater. Suddenly, Charlie Grimille who was supposed to be be hung on the gallows dies for real by hanging after a problem happens with the gallows used on stage.

The movie then fast forwards to the present day where years later another team of students are going to perform 'The Gallows' at the school theater. Reese is supposed to take the same role of Charlie, the guy who got hanged in 1993, and he will act alongside Pfeifer, a girl he has a crush on.

An unfamiliar woman with yellow hair always attended the performance of the play during training. The guys wondered who she might be. 

Ryan, Reese's friend, finds out that he has a crush on Pfeifer. After Ryan realized that Reese is doing the play just for her, he suggests that they go at night to the school's theater and ruin the settings so that Reese escapes the play without annoying Pfeifer.

The group smashed a few things then suddenly heard a voice, which turned out to be Pfeifer. After making up a story that Reese came to practice, they heard a strange voice, got scared then decided to leave, but to their surprise the door they came through was closed.

After getting frustrated because of the scary sounds and the fact that they can't leave, Cassidy exploded in anger and told Pfeifer about their original plan. Pfeifer got shocked, as she felt betrayed by Reese. (See Get Out (2017) Movie Explained)

After coming to a dark room, the group found a TV displaying a coverage of the real incident of 1993 and a group photo of the actors. They shortly realized that the strange woman who attended the practice was Charlie's girlfriend (the guy who died by hanging).

Reese found a group photo and recognized his father who was supposed to play the role of Charlie, but he called in sick at the last moment, and so Charlie had to die instead. Reese started to believe that Charlie died because of what his father did (calling in sick). (See Alien Covenant Movie Explained)

A strange force pulled Cassidy from her neck, leaving burn marks on it. Ryan then got frustrated and started calling Charlie's name then shortly he disappeared after the ghost dragged him from his neck using the rope of the gallows. Shortly, the same happened to Cassidy.

The hangman from 'The Gallows' started chasing Pfeifer and Reese who were trying to find a way out. They came across the bodies of their friends while running then finally found a way out. After going out of the building, Reese looked behind and found that Pfeifer didn't make it.

Reese suddenly realized that he had to sacrifice himself to save Pfeifer, as the ghost of Charlie wanted to kill him because his father, who called in sick, was responsible for his death. Reese and Pfeifer repeated the lines of the play and he helplessly walked to the gallows to face his death.

As Reese was about to be hanged, he realized that Pfeifer was still saying the words of the play. Reese was then killed and the hangman went beside Pfeifer, took her hand and they both bowed to the audience. Only one woman was there and clapping who turned out to be Charlie's Girlfriend.

In the last scene, it became clear that Pfeifer is Charlie's daughter and that she, her mother (the strange woman) and the hangman (her father's spirit) have conspired to kill Reese because he was the one responsible for the death of Charlie (the father).

In the beginning of the movie, Pfeifer asked Reese to do the play because she wanted to kill him to avenge her father. Charlie's girlfriend & Pfeifer's mother, the strange woman, used to attend the practicing because she was waiting for the final moment of vengeance.