Rosemary’s Baby by Ira Levin

Rosemary Woodhouse and her struggling actor husband Guy move into the Bramford, an old New York City apartment building with an ominous reputation and mostly elderly residents. Neighbors Roman and Minnie Castavet soon come nosing around to welcome the Woodhouses to the building, and despite Rosemary’s reservations about their eccentricity and the weird noises that she keeps hearing, her husband takes a shine to them.

Shortly after Guy lands a plum Broadway role, Rosemary becomes pregnant—and the Castavets start taking a special interest in her welfare. As the sickened Rosemary becomes increasingly isolated, she begins to suspect that the Castavets’ circle is not what it seems…

Legion by William Peter Blatty

The sequel to The Exorcist, A young boy is found horribly murdered in a mock crucifixion, multiple priests found beheaded and exsanguinated; Is the murderer the elderly woman who witnessed the crime? A neurologist who can no longer bear the pain life inflicts on its victims? A psychiatrist with a macabre sense of humor and a guilty secret? A mysterious mental patient, locked in silent isolation?

Lieutenant Kinderman follows a bewildering trail that links all these people, confronting a new enigma at every turn even as more murders surface. Why does each victim suffer the same dreadful mutilations? Why are two of the victims priests? Is there a connection between these crimes and another series of murders that took place 12 years ago – and supposedly ended with the death of the killer?