Prince of Darkness (film) - Plot

Plot

A priest (Donald Pleasence) invites Professor Howard Birack (Victor Wong) and a group of academics and students to join him in the basement of an abandoned Los Angeles church, where he requests their assistance in investigating a mysterious cylinder containing a constantly swirling, green liquid. Among those present is Brian Marsh (Jameson Parker), a student in metaphysics.

After researching the text found next to the cylinder, it is discovered that the liquid is the corporeal embodiment of the Anti-Christ. The liquid appears sentient, producing increasingly complex data that is revealed by computer decoding to include differential equations. Over a period of two days, small jets of liquid escape the cylinder and possess the group one by one to use them against the remaining survivors. Attempts to escape the building are thwarted by a mass of possessed street people who surround the building, barricade the doors from the outside, and kill two of the group.

Birack and the priest theorize that the being within the cylinder is actually the son of an even more powerful force of evil, the "Anti-God", who is bound to the realm of anti-matter. The survivors also find themselves sharing a recurring dream (apparently a tachyon transmission sent as a warning from the future year "one-nine-nine-nine") showing a shadowy figure emerging from the front of the church. The shaky transmission with the shadowy figure seems to change slightly with each occurrence of the dream, revealing progressively more detail. The narration of the transmission each time instructs the 'dreamer' that they are witnessing an actual broadcast from the future, and they must alter the course of events to prevent this occurrence.

Eventually, the cylinder opens and the remaining liquid is absorbed into the body of Kelly (Susan Blanchard), one of the students who becomes the physical vessel of the Anti-Christ: A gruesomely disfigured being, with powers of telekinesis and regeneration, who attempts to bring the Anti-God through a dimensional portal using a mirror, initially failing because the mirror is too small.

At the climax of the film, Kelly finds a larger wall mirror, and begins to draw the Father's hand through it as most of the group are immobilized by fights with the other possessed members. Marsh's lover, Catherine Danforth (Lisa Blount), is the only one free to act, so she tackles Kelly, causing both of them to fall through the portal. The priest shatters the mirror, trapping Kelly, the Anti-God, and Danforth in the other realm. Danforth is seen briefly on the other side of the mirror reaching out to the portal before it closes, leaving her in darkness. Immediately the possessed die, the street people wander away, and the survivors are rescued, relieved that the evil has been thwarted.

At the end of the film, Marsh has the recurring dream again, except now an apparently possessed Danforth is the figure emerging from the building. Marsh appears to awaken, rolling over to find a gruesomely disfigured Danforth lying in bed with him. Marsh awakens, screaming, and then recovers enough to approach his bedroom mirror, hand outstretched. The film cuts to black just before his fingers touch the mirror.