Read the excerpt from "The Legacy of Billy Mason."
Outside, the windmill continued its eerie creaking and moaning, and the light of the moon scarcely penetrated the dirt on the glass in the only window in the bedroom. Lying there in the darkness, Billy looked at the door again and again. What was behind it? Did it hide some awful secret? Did something monstrous lurk there? Then suddenly, as he watched, the door slowly opened, and as it opened, he saw his own name glowing in the darkness: Billy Mason.
What can the mood of the excerpt best be described as?
tragic
lighthearted
nostalgic
mysterious