Gabriel Shaw, an escaped inmate from Peakmore Psychiatric Facility for the criminally insane, breaks into Castle’s P.I. office with an ax and falls dead in front of Hayley and Alexis. Gabriel was convinced he was on a mission from God and tried to kill Warren Crown and his entire family 20 years ago. 

Castle finds a bible in Gabriel’s room with pictures of demons drawn on every page. Gabriel’s body has bible versus and latin words drawn on it. The wound that killed him has sulfur (otherwise known as brimstone) traces left inside and was made by a talon. 

Castle thinks a demon is involved in the murder. Gabriel used to be a spiritual adviser for P.I. Noah Cramer who used to have Castle’s office. Later, Noah was killed, impaled on a pipe at a construction site. 

Castle thinks that Shaw was trying to get to the safe in the office. Castle has never opened the safe. He has Hayley break in and finds a hidden passageway with a huge room filled with religious statues and other artifacts. The writings say that the End of Days is in two days time. 

Castle thinks that Shaw believed that Warren and Alice’s son, Victor was the antichrist. Victor’s parents were killed and Victor turns 30 and inherits his parents millions in two days. Crown runs a clean water initiative which will begin in two days. They use sulfur in the cleaning process for the water. 

Castle sees a strange light at his throat in all photos and videos. He thinks he’s marked for death.  He’s even more convinced when equipment almost falls on his head in the street. 

The ink used to write on the victim was anointing oil. Carl Von Ecklund once wrote to Shaw telling him he would use it on him when it was his turn to battle evil. Carl has died but his son, Oscar, lives in his apartment. He says he doesn’t believe the way his father did but he sells “blessed crap to suckers.” He also wrote the bible verses on Shaw for $50. 

Ryan and Espo find video of Shaw walking the streets with a man who appears and disappears behind him. Castle thinks it’s a demon but Beckett believes it’s due to the thunderstorm. 

Castle finds the globe in his loft spinning in the middle of the night for no reason but it’s just Beckett scaring him. 

Castle finds the angel dagger, the only thing that can kill the antichrist, in the safe in the middle of the night. Then he hears something and sees red glowing eyes and thinks the antichrist has come for him. Castle is knocked out and someone steals the dagger. 

Ryan and Esposito find the dagger at Noah Cramer’s widow’s home. Shaw destroyed her family 20 years ago. She stabbed him with a garden claw when he came to her home and wouldn’t leave. However she didn’t steal the dagger from Castle’s office. 

Turns out Oscar Von Ecklund stole the dagger and tries to use it to kill Victor Crown until Castle stops him. Back at the precinct, Beckett shows Castle that the “death mark” that keeps showing up in pictures near his throat is simply a reflection from his jacket’s zipper.