This is one of John Carpenter’s lesser-known works, and there’s a reason for that. It isn’t up to the standard he established with his better films. Even so, it has some interesting ideas and is worth checking out if you’ve never seen it, or revisiting if you have.
Here’s the skinny: Some seven million years ago, the Devil got turned into swirling green goo and imprisoned in a glass cylinder, basically a giant test tube. This test tube full o’ evil was locked up in a church beneath a church, watched over by a bunch of priests belonging to an order called the “Brotherhood of Sleep” who all dream the same dream every night. This “dream” is in actuality a message being beamed back to them from some point in the future, and warns them that the evil goo is going to escape its container. Cut to the present day (1987) when the goo does in fact escape. It starts possessing the members of the crew comprised of clergy and grad students specializing in quantum physics and turning them into zombies. The zombies attack the other members of the team to make more zombies, and it’s all so one of them can reach through a mirror and bring the Devil’s “father” through into the physical world. Oh, and apparently Jesus was an alien.
In terms of plot, then, PRINCE OF DARKNESS is kinda all over the place, but the bigger weakness is that none of the characters stand out, not even Donald Pleasance as a loony priest, and the evil goo isn’t enough of a leading man to carry the movie on its own. Had this one been titled THE EVIL GOO and been done tongue-in-cheek like BIG TROUBLE IN LITTLE CHINA it would have been a masterpiece.