Prince of Darkness is a 1987 American supernatural horror film, written, co-scored and directed by John Carpenter, and starring Donald Pleasence, Victor Wong, Jameson Parker, and Lisa Blount. The second installment in what Carpenter calls his "Apocalypse Trilogy"—which began with The Thing (1982) and concludes with In the Mouth of Madness (1994)—the film follows a group of quantum physics students in Los Angeles who are asked to assist a Catholic priest in investigating an ancient cylinder of liquid discovered in a monastery, which they come to find is a sentient, liquid embodiment of Satan.

Plot

Centuries ago in the Middle East, the Brotherhood of Sleep—a secret order of the Catholic Church—discovered a massive cylinder containing a swirling green liquid. Hidden even from the Vatican, the relic was eventually moved to Los Angeles and guarded in secrecy. In the present day, the last surviving member of the order dies before warning the cardinal that "the sleeper awakens." A Catholic priest sent to examine his belongings recovers a key that leads him to the cylinder, concealed beneath Saint Goddard's monastery.