In this ghastly story beginning in media res of a strange, isolated railroad employee, whom the unnamed narrator encounters as he treks downward from a ridge, Charles Dickens expresses his disdain for the technology of the new Industrial Age. With his first encounter with this man, the narrator finds him edgy and haunted by an idea; moreover, he is daunted by the signal-man. Nevertheless, he talks with the man after he steps back and the signal-man seems fearful of him, dispelling the narrator's trepidation for this man.
On a subsequent visit, the narrator learns that the signal-man was very disturbed by the narrator's first call to him because the words were exactly the same as those he has heard before. Perhaps to better explain himself, he narrates some of his past: he was formerly a student of natural philosophy, but he squandered his opportunities and has come to this repetitious job just like so many others who work in factories performing menial tasks well below their talents. At any rate, the signal-man explains that on a night on which the moon was bright, he heard someone cry out, "Halloa! Below there!" Startled, the employee looked up and saw someone standing by the red light which hangs near the tunnel; he was waving frantically and warning the signal-man to "Look out! Look out!" Then the man calls out, "Halloa! Below there! Look out!"
Because he admits to being very troubled by this vision, the narrator feels that the signal-man could use some professional help, which he offers to bring him on his next visits. However, when the narrator again comes by the lonely location, he discovers to his horror that the signal-man has died in a terrible accident. On this scene are investigators and a train engineer who relates that he yelled to a figure on the tracks, "Below there! Look out! Look out!" These words are eerily close to what the signal-man has related to the narrator. Then, when he hears the engineer says that he yelled out "Halloa! Below there!" and covered his eyes and continued to wave his other until the end. Further, the engineer expresses his wonder that the signal-man did not heed his warnings because the man was always so diligent and cautious.
What is so eerie is that what has happened to the signal-man is precisely what he has feared, but above this, not only were the words of the engineer precisely what the signal-man had told the narrator, but in a bizarre coincidence
...also the words which I myself -- not he -- had attached, and that only in my own mind, to the gesticulation he had imitated.