A woman answers a help wanted ad to be a housekeeper in a mysterious high-rise in New York City, not realizing she is entering a community that has seen a number of disappearances over the years and may be under the grip of a Satanic cult.
somewhat, Maria is implyed to have given a sexual ‘favour’ to a boss when employed as a cleaner but nothing is shown on screen and age is not mentioned
No significant flashing lights. There is a scene with some flames against a dim background, and once a character fires a shotgun to partially light up a room, but no strobing or major flickering. The end credits are a series of drawings that do kind of flash by, but they're nothing to worry about missing.