Everyone who lives at the Marshall Heights tower block knows one thing: never, ever answer the door if someone knocks at 3am.Arriving at Marshall Heights to search for her missing aunt, Megan Booth immediately starts to notice that something isn't right about the place. All the residents seem nervous, and no-one seems to have a clue what happened to her aunt. And then there are the strange figures that are sometimes spotted at night on the train tracks that run past the building.As Megan searches for answers about her aunt's disappearance, she learns that the ghosts of Marshall Heights seem to have their own agenda. Meanwhile, a young girl living in another of the flats finds herself drawn closer and closer to a strange darkness that waits in the basement. Why are there piles of human teeth in the shadows? And who keeps knocking at the door, calling out for help using the voice of a dead man?3AM is the story of a group of people living in a haunted building, and their gradual realization that someone or something is trying to break through from the world of the dead.