As you've probably already guessed, the Conjuring movies, while based on Ed and Lorraine Warren's actual investigations, don't exactly follow reality beat by beat. The Conjuring: The Devil Made Me Do It, or The Conjuring 3, is no exception. The latest addition to the Conjuring universe follows the infamous 1981 case of Arne Cheyenne Johnson (Ruairi O'Connor), a young man who claimed in court that the devil made him kill his landlord Alan Bono. The film doesn't go through Johnson's legal proceedings with a fine comb — the horror movie focuses more on how an occultist named Isla (Eugenie Bondurant) curses Johnson and his girlfriend Debbie Glatzel's (Sarah Catherine Hook) family. Johnson and the Glatzels are very much real people, but is the occultist an actual person? Long story short, Isla appears to be a fictional character who's used to propel the film's plot forward.
So, what's real in The Conjuring 3? Before Bono's murder, the Glatzels really did get in touch with the Warrens to help their 11-year-old son, David, who they believed had been hosting a demon (or, more accurately, 43 demons). The real-life Johnson also dared whatever was inside of David to enter him. After Johnson committed the murder, he later used demonic possession as a defense in court but was still ultimately convicted of manslaughter.
While grounded in a real story, The Conjuring 3 definitely takes creative liberties in its storytelling. The movie's plot really hinges on how the Warrens find a creepy satanical totem underneath the Glatzel home. When the Warrens investigate the case of a dead girl named Katie Lincoln (a fictional character who is also stabbed 22 times like Johnson's landlord), they connect her death to Johnson's crime after tracking down the body of Jessica Louise Strong, the friend who killed her. Using her sensory gifts, Lorraine locates the occultist after touching Jessica's corpse.
And here's the twist: Father Kastner (John Noble), whom the Warrens originally come to for help, is actually the occultist's, or Isla's, father. Kastner lets Lorraine into the tunnels where Isla operates her satanic activities, only to be killed by his daughter soon after. Ed ultimately destroys Isla's altar, and a demon ends up taking Isla because she promised it a soul.
At the end of the day, most of The Conjuring 3 is movie magic, or dark occultist magic, if you will — but with plenty of fun horror movie Easter eggs to spare.