Two teenage boys are recording their exploration of the abandoned Gonjiam Psychiatric Hospital, where rumor states that the director of the hospital killed all of the patients and went missing. The two head to Room 402, the intensive care unit, which no one has opened before. They try to open the door but suddenly hear a ping pong ball. Their broadcast abruptly ends. After seeing news of the teenagers' disappearance, Ha-Joon, the owner of YouTube channel "Horror Times", decides to explore the building as well.Ha-Joon gets together a group of six people: three girls; Ah-Yeon, Charlotte, a Korean-American and Ji-Hyun, and three boys; Sung-Hoon, Seung-Wook and Je-Yoon. They will do a live broadcast of their exploration of the hospital with a goal of reaching one million viewers.The group travels to the hospital and set ups their equipment. Ha-Joon stays at their base camp off the road to control the broadcast. The rest of the group find some underwear and tie it to a tree as a marker. Upon breaking in, Charlotte pours holy water in a small petri dish to record its reactions. In the director's office, they find a group photo with all the patients and staff. Ji-Hyun and Charlotte explore the laboratory, where they find a doll. The team performs a ritual to 'invite' the spirit out but become terrified when the strings with bells that they had set up start to shake. However, it is revealed to have been staged by Seung-Wook and Sung-Hoon, unbeknownst to the other four, as a way to attract more viewers. Going back to the lab, Charlotte and Ji-Hyun are shocked to find that the doll has moved. The group discover it is the same doll held by one of the patients in the group photo.Je-Yoon and Ah-Yeon try to open the door to Room 402, while the other four explore the "Group Treatment Room," seeing many strange coffins. Seung-Wook puts his hand inside a hole in a coffin and fakes his hand being pulled. However, when Ji-Hyun tries the same, her hand is actually pulled and wounded with claw-like scratches. The group, terrified, flees. Too disturbed, Ji-Hyun and Charlotte decide to leave. Ha-Joon reviews footage of all six participants standing together and becomes unsure who filmed it if all six are in the shot.Charlotte and Ji-Hyun walk back to the base camp but end up caught in an illusion as they encounter the underwear marker more than once. Ji-Hyun goes into a trance. Suddenly, her eyes open with black sclera. Charlotte realizes she is in Room 402. Ji-Hyun is in a corner with the doll from the lab by her feet. A naked man appears in front of her and Charlotte is attacked and pulled into the darkness.Seung-Wook and Sung-Hoon see a wheelchair pushing itself in the basement. Everything in the room begins to float, and both boys are knocked out. Regaining consciousness, Sung-Hoon runs to Je-Yoon and Ah-Yeon, who are still drilling to open the door to 402. Suddenly, a ping-pong ball bounces towards them and Charlotte's screaming is heard from inside 402. The infra-red cameras starts to flash as the sensor detects a presence. The door of 402 opens and the screen goes dark.Sung-Hoon, Je-Yoon and Ah-Yeon find themselves trapped in a dark room with no exit, standing in knee-deep water. Numerous ghosts appear; the three panic until they are possessed one after the other and swallowed by the darkness. Ha-Joon, after losing contact with his team, goes to investigate. He brings a drone and flies it upwards, seeing someone in the window. However, he realizes it was an illusion. The person in the window was himself. He turns to see the director's body floating as if hanged. Ha-Joon is then strangled to death. Regaining consciousness, Seung-Wook finds himself strapped to a wheelchair. The wheelchair slowly rolls to Room 402 by itself, and Seung-Wook cries out for his teammates. He sees various ghosts and hears gibberish before he is pulled into 402.The live broadcast fails with viewers dropping and claiming the broadcast was fake. In the epilogue, the dish of holy water starts to boil, implying holy water has the effect to repel ghosts.