HenryTownshend finds himself locked in his apartment in for five days with no means of communication and having recurring nightmares.[11] Shortly afterwards, a hole appears in the wall of his bathroom, through which he enters alternate dimensions. He ends up in an abandoned subway station, where he meets Cynthia Velasquez, a woman convinced she is dreaming and who is soon killed by an unknown man.[19] Awakening in his apartment, he hears confirmation on his radio that she is indeed dead in the real world.[20] Similar events repeat with the next few people Henry finds: Jasper Gein, a man fascinated with the paranormal and the cult of Silent Hill;[21] Andrew DeSalvo, a former employee of an orphanage run by the aforementioned cult;[22] and Richard Braintree, a resident in Henry's apartment complex.[23] All the deaths bear similarities to deceased serial killer Walter Sullivan's modus operandi.[24]
Henry finds diary scraps belonging to journalist Joseph Schreiber - the former inhabitant of his apartment - who was investigating Walter's murder spree.[25] He discovers that Walter is an orphan who has been led to believe his biological mother was in Henry's apartment, where he had been found abandoned after birth.[26] To "purify" the area, Walter, now in an undead state, is attempting to perform a ritual, which requires twenty-one murders to be committed.[27] As Walter prepares to kill his twentieth victim, Eileen Galvin, a child manifestation of himself appears and stops him. Eileen agrees to join Henry in locating Joseph.[28] At the same time, supernatural occurrences begin to manifest in Henry's apartment. The two eventually find Joseph's ghost, who tells them that the only way to escape is to kill Walter, and reveals that Henry is the intended twenty-first victim.[27]
Shortly after Henry acquires Walter's umbilical cord, which they require to kill him, Eileen leaves Henry and returns to his apartment.[27] Henry follows and finds her, possessed and about to walk into a deathtrap, and a fight between Henry and Walter ensues. There are four possible endings, determined by whether or not Eileen survives and the condition of Henry's apartment.[4] The "21 Sacraments" ending sees Walter and his child manifestation in his apartment, while the radio reveals that Henry and Eileen have died, along with several others.[29] In "Eileen's Death," Henry awakens in his apartment, and learns from his radio that Eileen has died, to his sorrow.[30] In "Mother," Henry escapes from his apartment building, and brings flowers to Eileen, who plans to return to the apartment building. His apartment, meanwhile, has become completely possessed.[31] "Escape" begins similarly to the "Mother" ending, but Eileen resolves to find a new place to live, and his apartment is not shown to be possessed.[32]