Who does Mary in "Lamb to the Slaughter" talk to at the grocery store?
Mary goes to the grocery story mainly to establish an alibi. She knows that she can't have been present in the house when Patrick was killed because she would have heard something. She wants it to look as if she went to the store and the murderer took advantage of her absence to slip inside and kill her husband while there was no witness present. Otherwise, the murderer would have had to kill Mary too, and she has to account for the fact that she is still alive.
The grocery store is one of those small, old-fashioned shops run by one man who knows all his customers and has time to chat with all of them. It is a far cry from the modern supermarket, as described by John Updike in his story "A&P." The grocer's name is Sam. He and Mary know each other pretty well. Naturally she spends as much time there as she can, allowing the fictitious murderer to slip inside, hit Patrick over the head with a blunt instrument, and make his getaway.
Mary makes her selections item by item. None of them seems really necessary. She buys some potatoes and a can of beans and finally a piece of cake. If the police had been at all suspicious of her, they might have checked her cupboards and refrigerator and found that she already had plenty of potatoes and plenty of canned vegetables. She is a woman who stuffs her husband with food, and she would certainly have plenty on hand without running to the grocery store.
The author Roald Dahl explains several times that the Maloney's always go out for dinner on Thursday nights. This is obviously intended to account for the fact that Mary might have to go to the grocery store at the last minute because Patrick wants to stay home on that particular Thursday night.
"Patrick's decided he's tired and he doesn't want to eat out tonight," she told him. "We usually go out on Thursdays, you know, and now I don't have any vegetables in the house."
This is a weak spot in her alibi. If Mary uses canned vegetables, a woman like her would have plenty of cans of vegetables in her cupboard. If the police had suspected her of killing Patrick, they might have asked her what she bought at the grocery store and then checked her cupboards and refrigerator to see if the trip to Sam's had really been necessary. But Roald Dahl takes pains to establish that Mary and Patrick are considered to be the perfect married couple, so the police never suspect her. This is, of course, very helpful to the author's story.
Even though Mary is apparently the quintessential loving, devoted wife, there are several reasons why the police might have suspected her. One is that the police always suspect the spouse when the other spouse gets killed. The second is that there was such a narrow window of opportunity for the unknown perpetrator to do the deed. The third is that she supposedly had to run out to purchase things which she should have already had in her kitchen. Another is that the unknown perpetrator's behavior is uncharacteristic. Was he supposedly peeking through the window and waiting for an opportunity to kill Patrick when he was alone? Wasn't it convenient for the murderer that Patrick decided not to go out to dinner that Thursday night when they always went out on Thursday nights? And wasn't it a break for the murderer that Mary had to run to the grocery store to make those last-minute purchases? What would the murderer have done if she hadn't gone to the grocery store for just enough time to enable him to kill Patrick? One other thing: Why would Mary decide to cook a leg of lamb for dinner? It wasn't even thawed. It would have taken a full four hours to cook that leg of lamb. Patrick got home at five. They wouldn't have been able to eat dinner until nine o'clock,which is late for such a couple, especially when the husband is tired.