As "The Red Room" is told in the first person, the tone reflects the attitude of the main character. The narrator's determination to be "rational" comes across in the ordered, detailed, analytical, and somewhat removed descriptions he gives. This applies not only to the house and the things he sees. But it also applies to the narrator's own mental states, and the motivations behind his actions. Doesn’t this just sound like a scientist: "I resolved to make a systematic examination of the place at once, and dispel the fanciful suggestions of its obscurity before they obtained a hold upon me" (32). Because of the narrator’s commitment to being rational and clear-headed, he looks down upon anything that seems superstitious or fantastic. This disdain comes across in his dismissal of the "fanciful suggestion" of the room. Or the old people, who he says are prey to "fashions born in dead brains" (28).
In spite of his claims to being rational, a nervousness and sense of foreboding does creep into the narrator’s tone as the story progresses. We see this first in the unease and mysterious suggestiveness of some of his descriptions, as when he says the shadows in the red room make "that odd suggestion of a lurking, living thing" (33). As he grows more frightened, we see shorter sentences and more frantic, exaggerated language: "I leaped panting and disheveled from candle to candle, in a vain struggle against that remorseless advance" (43). Still, by the time the narrator gets knocked unconscious, we’re a long way from over-the-top hysteria, and the tone maintains a certain distance from the utter panic the narrator is feeling at that moment.