In The Night of the 8th Day, a former exorcist named Park Jin-soo becomes the key to stopping an ancient evil from resurfacing. Over two thousand years ago, two malevolent beings were sealed in caskets, and their resurrection requires them to possess seven human hosts. When one of these beings begins to awaken, Monk Ha-jung, the guardian of one of the caskets, seeks out Park Jin-soo, who is destined to stop them. With the help of Monk Chung-seok, Jin-soo embarks on a desperate mission to find and destroy the demon before it wreaks havoc on the world, in a race against time that blurs the line between the real and the supernatural.