Globe-trotting occult investigator Kyle Hawkes’s most recent film series examined a notorious case of demonic possession; the mystery of a priest named Father Zacharias Stilicho, who renounced the Church and disappeared after performing an exorcism, leaving behind only cryptic clues about glimpsing something called Carcosa.

Lured to a castle in northern Italy, he and his fiancé Ella are imprisoned by the wealthy recluse Baron Vassago, who has spent years searching the world for the missing priest. Convinced that the heretic possesses forbidden knowledge, he’s prepared to go to any lengths to learn the secrets of such power—including murdering Kyle’s friend and producer.

Kyle is faced with a chilling ultimatum: find the priest or Ella dies too. He embarks on a harrowing journey across Europe, but locating Father Zacharias is only the first hurdle. While the two form an alliance, hatching a daring plot to save Ella and defeat Vassago, Kyle realizes too late that the rogue priest is using all of them to accomplish the one thing he’s been trying to do for years: To summon the King in Yellow.