The climax, or the point of highest emotional intensity, in "The Signal-Man" by Charles Dickens is the narrator's horrified sense that the ghosts of which the signal-man has spoken to him have a reality apart from the individual imagination.
Dickens's ghost story is one that edges the Gothic. In the exposition of the story when the narrator happens upon the signal-man and calls to him, instead of looking up toward the sound, the strange man peers down the line of the railroad tracks. The narrator finds "something remarkable" in this behavior. And, indeed, the "remarkable" eventually happens in this narrative of Dickens.
Moreover, it is this "remarkable" behavior that is involved in the climax of the story. For, when the narrator, who has established a relationship with the lonely signal-man, returns in order to accompany the disturbed railroad employee to a doctor, he looks down from the same point at which he has first seen the signal-man and perceives a man imitating the exact gestures of his acquaintance's ghost. However, "the nameless horror" which the narrator feels soon passes when he realizes this man is real. Nevertheless, the narrator's emotions are again raised, and this time they approach the intensity of climax:
...with a flashing self-reproachful fear that fatal mischief had come of my leaving the man there, and causing no one to be sent to overlook or correct what he did....
the narrator descends and, horrified, he learns that the signal-man has been killed. His fears are confirmed as the narrator realizes that the ghosts have possessed a reality beyond the signal-man's imagination.