In "Lamb to the Slaughter," Mary Maloney kills her husband by striking him across the head with a frozen leg of lamb. She then proceeds to cook the lamb in the oven while the police are in her house, investigating the death. She even manages, at the end of the story, to get the police officers to eat the lamb, and in eating the lamb the police officers destroy the evidence that they are supposed to be finding. This simple outline of the plot suggests a story which is a little bit surreal, and this plot in itself influences the tone of the story. Because the plot is so strange, it is difficult as a reader to read it in anything other than a slightly, darkly comic tone.
At the end of the story the police officers, while eating the cooked leg of lamb, talk about where the murder weapon might be. One of the officers says, "I think it's right here on the premises," and the other officer replies, "Probably right under our very noses." The dramatic irony here is so extreme that it's difficult as a reader not to laugh and thus not to read the ending in anything other than a comic tone. The comedy is of course of the dark variety as we are ultimately laughing along with a woman who has murdered her husband.
The tone of the story, as well as being comic, is also sometimes rather sinister. For example, when Mrs. Maloney arrives home with her groceries, she calls out for her husband. She calls his name and then says, "How are you, darling?" At this point of course Mary knows that her husband is dead. The tone of the story at this moment, therefore, becomes rather sinister. We wonder how Mary Maloney can behave in such a calm way, as if nothing has happened, given that she has not long since murdered her husband.