David has only a father with whom he lives in an old and shabby apartment building. He is very lonely, as is old Mr Alverston, their neighbour, who is afraid that he is losing his mind.
By accident Davis discovers that he can get into the ventilation shaft of the building and he begins to spy on the people in the other apartments. One day he comes to face with a ghost, at first friendly, but more and more terrifying. Soon it becomes clear that David an Mr Alverston are both in great danger.