What does the domestic setting contribute to the story "Lamb to the Slaughter?"

The domestic setting of Roald Dahl's short story "Lamb to the Slaughter" presents a scenario in which gender roles thrive within their socially-specific parameters. The setting also gives us a glimpse into the lives of the Maloney's and shows us that Mary is invested in her lifestyle to a fault, particularly when she realizes that life as she knows it may never be the same again. Additionally, the setting represents everything that is important to Mary, thus driving her to make the ultimate choice to preserve what she treasures most. 

Within the story's setting, the characters play their gender-based and family roles on a daily basis: Patrick embodies the role of "the man of the house." He is a provider, head of household, husband, and future father. He also epitomizes manliness: He is a strong and seemingly dedicated police officer - a protector of the safety and security of the people. 

Similarly, Mary's character represents the idea of angel of the household. This construct of the Victorian era, first seen in the eponymous poem written by Coventry Patmore in honor of his wife, Emily, bestows upon women unrealistic expectations. Women are portrayed essentially as agents of domestic bliss. Under this construct, they are seen mainly as submissive wives, mothers, and nurturing homemakers whose sole pleasures in life derive from the "joys of womanhood" that are thought to be born out of homely activities. 

This being said, the setting of the story fits perfectly the characters of Patrick and Mary. Their household, as described by Roald Dahl is, indeed, a product of its "angel." This not only because Mary keeps her home clean and organized, but also because the condition of the home mirrors the condition of Mary's perception of reality: one where there is nothing but warmth, love, protection, predictability, hope, and financial safety. 

The room was warm and clean, the curtains drawn, the two table lamps alight-hers and the one by the empty chair opposite. On the sideboard behind her, two tall glasses, soda water, whiskey. Fresh ice cubes in the Thermos bucket. Mary Maloney was waiting for her husband to come him from work.

It comes to no surprise that, upon hearing that her husband will leave her, the entire foundation of Mary's state of mind crumbles down in a way that would mirror how her whole lifestyle will similarly follow. As such, she must protect the warmth and security that she is so fond of. To her, it is a matter of life or death. 

Therefore, the setting contributes in many ways. First, it mirrors the state of mind of Mary Maloney; it embodies safety, love, and marital bliss. Second, it is the most important thing to Mary Maloney: It is her home, her fortress. Third, it is the scenery where the Maloney's get to display their socially-expected roles to perfection: He, as the head of household, and she as the angel of such household. The threat against such a setting of bliss and perfection means life or death to Mary. It is not surprising that she makes the choices that she makes.