While Thomas' spirit half is confident that Thomas would never hurt Lilianne, he is unaware of Thomas' current whereabouts. Eventually the Maw broke out of the bunker and caused the Niwa Massacre. However, this did not stop Lilianne's powers from going out of control and after she was raped by Richard, she created the Maw as the manifestation of her tormented soul. He explains to Marianne that Lilianne had trouble controlling her own powers, so Thomas kept her confined in the bunker. Marianne discovers a fallout bunker hidden beneath the ruins of her family home where she encounters Thomas' spirit half. Marianne comes to realize that she is Thomas' youngest daughter, having into a coma from the fire and Thomas leaving her at the hospital while he remained with Lilianne at Niwa. Eventually he had fled back to Poland and hid at Niwa, eventually starting a family, but an agent of Służba Bezpieczeństwa named Henry discovered Thomas, subdued him, and forced him to watch as he set fire to Thomas' home with his children inside, causing Thomas to attack and murder him.

Marianne pieces enough clues together to learn that Thomas was also a medium and due to this was experimented on by Nazis and Soviets who found out that his powers could be used to sever people's minds from their bodies. Through her visions, Marianne finds out that Sadness is a spirit of Lilianne, who was molested by Thomas' older and trusted friend Richard. Marianne repeatedly offers to send Sadness to her peace, but she refuses. In the spirit world, she encounters Sadness, the spirit of a young girl who warns her of the Maw, a hostile and malevolent spirit that has managed to partially exist in the real world and was responsible for the Niwa Massacre by occupying human hosts and using their bodies to murder others, now hunting down Marianne to sate its hunger and escape Niwa. While exploring Niwa, Marianne finds the place has strong ties to the spirit realm, and evidence that Thomas, the resort's manager, and his daughter Lilianne were at the epicentre of the Niwa Massacre. However, he is only willing to talk if Marianne agrees to meet him at the Niwa Workers' Resort, an abandoned communist-era vacation resort in the Polish wilderness, and which had been shuttered by the government after an event called the Niwa Massacre years earlier, where a large number of people were murdered and the survivors fled the area. Thomas offers to explain the origin of Marianne's powers, as well as the meaning of the dream. While grieving over the death of her foster father, Marianne receives a mysterious phone call from a man named Thomas, who knows of her abilities. Marianne, a spirit medium that helps troubled souls seek final respite, has a recurring dream of a man shooting a young girl by a lake. The Medium is set in post-Communism Poland in 1999. Her psychic abilities may also be used against hostile forces and are recharged by interacting with energy spots called spirit wells. Being able to inhabit both worlds aids puzzle solving. The Medium is a psychological horror game played in third-person as Marianne, a medium who can travel into the spirit realm. A puzzle is solved between realities, unveiling a spirit well.

The maw the medium