Prince of Darkness is a 1987 American supernatural horror film, written 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

A Catholic priest invites quantum physicist Professor Howard Birack and his students to join him in the basement of a Los Angeles monastery belonging to "The Brotherhood of Sleep", an old order who communicate through dreams. The priest requires their assistance in investigating a mysterious cylinder containing a swirling green liquid. Among the thirteen academics present are wise-cracking Walter Fong, demure Kelly, the highly-strung Susan Cabot, and lovers Brian Marsh and Catherine Danforth.