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 large cylinder of swirling green liquid. Kept secret from even the Vatican, the cylinder was eventually moved to Los Angeles, where it has since been guarded by the Brotherhood. In the present day, the orders' last member dies before he can warn the cardinal that "the sleeper awakens." A Catholic priest recovers a key from his possessions, which leads him to the cylinder’s hiding place beneath Saint Goddard monastery.