When we are looking for the tone of a piece, we look at the way the author uses language to create a feeling or image in our mind. To create a dark and tragic tone, the author will use words that give us a sense of discomfort, unease, and despair.
In The Monkey's Paw, what about the setting gives us these feelings? The author describes the night as "cold and wet", he describes the house as having echoes throughout, and it ends with a quiet and deserted road, lit only by a streetlight across the way.
What language gives us these feeling in the character's interactions with each other? The author uses phrases such as "an unusual and depressing silence" that falls between them. When the news about their son arrives, the woman's "face was white, her eyes staring, and her breath unheard". Neither of the older couple spoke while waiting for something to happen in the third part, but simply listened to the empty house and the ticking of the clock.
Imagery like this is what an author uses to create the tone of the piece. Often, the author will not outright tell you that the woman was frightened or crazed with grief. Instead, this author describes her cries that can be heard throughout the house, that the darkness was depressing, or that her hands were shaking.
