Inside the game-changing 'Exorcist' twist you didn't see coming

At first glance, the TV iteration of The Exorcist seemed completely unconnected to the 1973 film that has terrified audiences for decades, but Friday's episode of the Fox thriller revealed that the show isn't a reimagining -- it's a sequel.

The final moments of episode 5, "Through My Most Grievous Fault," dropped the bombshell that Geena Davis' character, Angela Rance, is actually Regan MacNeil -- the 12-year-old girl who was possessed in William Peter Blatty's original novel and the subsequent film adaptation.

Just as Angela/Regan shared this shocker with Father Tomas (Alfonso Herrera) at church, her mother, Chris MacNeil (Sharon Gless) showed up on the Rance family's doorstep, looking for her daughter.

While Tomas and Marcus (Ben Daniels) had previously assumed that Casey's (Hannah Kasulka) possession was because the demon couldn't get at Casey's troubled sister Kat (Brianne Howey), it appears that the demon's true target is Regan, not her daughters.

And all of that came after Marcus and Tomas launched a visceral exorcism to try and free Casey, offering up some of the most chilling scenes attempted on broadcast television.

Below, Mashable has an exclusive look at the script pages from two pivotal scenes in episode 5, annotated by the episode's writer, David Grimm, and creator/executive producer Jeremy Slater.

First up, Grimm breaks down the pages from Casey's exorcism after Marcus kicks Tomas out and attempts to tackle the demon alone, offering fascinating insights into the disgraced priest's backstory.

Below, Slater reveals what went into crafting Regan's reveal to Tomas, including the show's twist on "Captain Howdy" -- the demon that Regan believed was her imaginary friend as a child -- and how they came up with the alias "Angela Rance," which gave us a clue to Regan's identity right from the start.

Is your mind blown?

The Exorcist airs Fridays at 9 p.m. on Fox.