made that the title also refers to him. Mary, however, is the viewpoint character and gets far more attention in the story from beginning to end. At first she is portrayed as an extremely meek and gentle woman, very much like a lamb.

Her skin--for this was her sixth month with child--had acquired a wonderful translucent quality, the mouth was soft, and the eyes, with their new placid look, seemed larger, darker than before.

... and she, on her side, was content to sit quietly, enjoying his company after the long hours alone in the house.

She is portrayed as exceptionally gentle right up to the point where she suddenly releases her pent-up anger at the man who is deserting when she is six months pregnant and after her years of slavish devotion.

Mary Maloney simply walked up behind him and without any pause she swung the big frozen leg of lamb high in the air and brought it down as hard as she could on the back of his head.

She might just as well have hit him with a steel club.

So the second meaning in the double entendrecould apply either to Patrick or Mary Maloney. It seems more likely that Roald Dahl intended it to apply to Mary, since she is the major character, the protagonist, and the viewpoint character; whereas he husband has only a minor role and is dispatched early in the story.

Roald Dahl's story is called "Lamb to the Slaughter" first because this is a traditional phrase for someone going innocently to their death. In ancient tribal cultures, a lamb was often sacrificed to atone for the sins of the tribe. This gave rise to the Christian idea that Jesus was a sacrificial lamb, going to his death for the sins of his people.

This religious tradition is undermined by the second reason for the title. In this case, the murder weapon is a frozen leg of lamb. The word lamb therefore refers both to the sacrificial victim and the instrument of his martyrdom. Patrick Maloney is not entirely innocent, since he had planned to leave his wife in a selfish and insensitive manner, making her seem like the injured party initially. However, one of the story's major themes is the deceptiveness of appearances. As the police officers sit down to eat the leg of lamb after searching for a murder weapon at the end of the story, it does not occur to them that, when frozen, this tender meat would have been as hard as steel. Nor do they dream of how Mary Maloney, who seems as innocent as the proverbial lamb, used it as a weapon.

I'm assuming you're asking what the narrative is about.

It is the tale of Mary Maloney and the perfect murder.  It is also the story of Mary's transformation from a docile wife whose very existence is devoted to her husband, Patrick, to a woman who is now able to take charge of her life.

Mary learns that Patrick is leaving her.  The reason is never clear.  This is distressing because she is pregnant and has no real means of income, though Patrick states he will look after her.

Not knowing what else to do, she begins to make supper, which happens to be a leg of lamb.  However, before she is cognizant of what she is doing, she bashes her husband over the head, killing him instantly.

Then she begins to plot how she can get away with the murder.  She rehearses what she will say to their butcher and heads to the store.  Appearing calm and collected, she gets the necessary things for supper.  When she returns home, she calls the police, who all happen to be friends of her late husband, who was an officer himself.

She states that she found him dead when she came back from the butcher.  The butcher is questions, but he states that she seemed quite normal to him.  It is clear they thing she might have done it, but she acts so genuine, they quickly underestimate her and rule her out as a suspect.

As the story ends, Mary asks the detectives to stay for supper and feeds them the murder weapon.

In some of the major religions (Judaism, Christianity, and Islam), lambs were sacrificed as a way to rid a person of his/her sins. The person would place his hands on the lamb, thus transferring his sins to the animal and the ritual killing would complete the transference. And the lamb itself would not know that it was about to be sacrificed. Both of these points are significant to the title of Dahl's story. 

Consider the notion of "sacrifice" in metaphorical as well as literal terms. Mary is the first sacrificial lamb. Waiting at home, perfectly content, she is led to be rejected by her husband, Patrick. She had no idea this was coming. And in a way, Patrick is relieved in confessing his sin to her. He basically transfers the burden of his sin on to her. 

Patrick is then literally sacrificed when Mary kills him. So, he is the next "lamb." The detectives are the next lambs because they are unknowingly led astray as well. Mary tricks them into eating the evidence (the leg of lamb). And although this does not absolve her sin, it does erase it in the minds of the detectives. So, in the eyes of the law, Mary has transferred her sin to some other potential suspect. 

One might also suggest that the reader is a potential fourth lamb. If the reader finds himself/herself rooting for Mary at some point, following the murder, the reader has been led (by Dahl) to root for a murderer. In each of these examples, each particular "lamb" is used, killed, or tricked. 

The lamb was used to kill Patrick. So, an actual lamb was sacrificed as well. And there is the overt reference to the nursery rhyme "Mary Had a Little Lamb." This allusion adds to the morbid humor of the story. Mary had a little lamb and she used it to kill her husband. 

In paragraph 16, Mary comments, "'I think it's a shame...that when a policeman gets to be as senior as you, they keep him walking about on his feet all day long."  So it seems that Patrick Maloney is of the police force but it never mentions that his position is anymore than that.  When the police arrive at the Maloney house to look into Patrick's death and possible murder, Mary recognizes many of the men, since her husband has been part of the force for a long time.  But the story does not mention that he is a detective or sergeant or captain or anyone with a more particular title.  It does also appear that Mary and Patrick have been married for some time if she knows his co-workers, yet she appears to be pregnant with their first child, as no other children are mentioned in the story.

Roald Dahl started with a good black-comedy idea: wife kills husband with a frozen leg of lamb, then cooks the lamb to dispose of the murder weapon. The story was written in the 1950s when Americans were buying big freezers and filling them with meat, thinking they could save money by buying in quantity at wholesale prices. The fad did not last. Electricity rates went up, there were power blackouts causing spoilage, and the frozen meat probably didn’t taste as good as fresh.

It was a stroke of genius to make Patrick Maloney a cop. This strengthened Mary’s alibi enormously because cops make many dangerous enemies. The investigators naturally supposed that Patrick had been the victim of some felon, or a friend, relative, or hit man hired by that felon. The Maloney house was full of cops because they were giving special attention to a murder of “one of their own.” They spent many hours searching for the murder weapon, giving Mary plenty of time to cook the lamb thoroughly.

The story might not have worked as well if Patrick had not been a cop. In inside domestic murders suspicion usually falls on the spouse. Dahl portrays Mary as being an exceptionally docile, devoted wife, so it would be hard to imagine her killing anyone with a heavy blunt instrument. But it would also be much harder to imagine some killer entering the home during the short time she was at the grocer’s if Patrick had not been a cop.

One wonders what a really good detective, like Columbo as played by Peter Falk on television, would do. The Columbo stories usually involved someone who planned the perfect crime, only to be trapped by a tell-tale clue. Columbo would have inspected the freezer. He would have taken out all the frozen meat looking for the murder weapon, and he would have noticed that the meat itself was rock-solid. This could have led him to suspect that the leg of lamb he smelled cooking could have made a perfect weapon in its frozen state. A leg of lamb is different from other roasts because the bone provides an ideal handle.

A good detective (which the investigating officers were not) might have found out that Patrick Maloney had some reason for wanting a divorce--although Dahl is careful to portray him as a strong, silent type.

She loved the intent, far look in his eyes …  and especially the way he remained silent about his tiredness, sitting still with himself until the whisky had taken some of it away.

There are several details apparently intended to suggest that he spends his evenings at home, so that he probably isn’t having an affair.

When the clock said ten minutes to five, she began to listen, and a few moments later, punctually as always, she heard the tires on the gravel outside…

Other details suggest that he keeps his thoughts to himself, so perhaps he hasn’t discussed his domestic relationship with anybody else.

“So there it is,” he added. “And I know it’s kind of a bad time to be telling you, but there simply wasn’t any other way. Of course I’ll give you money and see you’re looked after. But there needn’t really be any fuss. I hope not anyway. It wouldn’t be very good for my job.”

Mary is able to bring off a perfect crime because she is a devoted wife, her husband has no known reason for wanting a divorce, nobody knows he has asked for a divorce, the investigating cops are not super-sleuths, Mary knows how cops think because she is a cop’s wife, and she gets them to eat the murder weapon.

The more times that I am forced to consider the title of this story, the more I think it is the perfect title.  

First, Mary is initially presented to the reader as a lamb.  A lamb is typically docile, meek, and mild.  Mary is waiting in the front room for Patrick to come home.  Once Patrick is home, she attends to his every need and then quietly sits near him.  She is perfectly content to bask in his glorious manliness.  

She loved to luxuriate in the presence of this man, and to feel – almost as a sunbather feels the sun – that warm male glow that came out of him to her when they were alone together. 

She is the lamb and Patrick is the protector.  That is until Patrick decides to metaphorically slaughter Mary.  He tells her that he is leaving her, and she is left completely devastated and broken. She is a slaughtered lamb.  

Mary goes to get dinner started in a daze.  She's practically a walking zombie.  Then Patrick announces that he is going out to dinner.  That's when the title of the story shifts meanings.  Mary is now the lamb coming to do the slaughtering. She is not the lamb to be slaughtered anymore.  She is the lamb to the slaughter of Patrick.  What's even better is that she brings an actual lamb to the slaughter.  Her murder weapon of choice is a leg of lamb.  

At that point, Mary Maloney simply walked up behind him and without any pause she swung the big frozen leg of lamb high in the air and brought it down as hard as she could on the back of his head.

The title is intended to make the story seem amusing, not to be taken too seriously even though it is a murder story. The title "Lamb to the Slaughter" has several different possible interpretations. 

First, Mary Maloney uses a frozen leg of lamb to kill (slaughter) her husband Patrick?

Second, Patrick is caught completely off guard. This makes it easy for Mary to hit him over the head from behind. The way Patrick gets killed alludes to a passage in the Old Testament:

He was oppressed, and he was afflicted, yet he opened not his mouth: he is brought as a lamb to the slaughter, and as a sheep before her shearers is dumb, so he openeth not his mouth.           Isaiah 53:7

And finally, Mary has always behaved as meekly as a lamb. It is a big surprise when she suddenly kills her husband in a moment of rage. She uses the weapon which happens to be in her hand, a frozen leg of lamb.

The whole story is based on the fact that the murder weapon is a frozen leg of lamb. The police look all over for a murder weapon but are unable to find one because Mary put the leg of lamb in the oven and turned the oven to the highest temperature. The investigating officers end up eating the evidence without realizing it. One of them says:

"Personally, I think it's right here on the premises."

Another comments:

"Probably right under our noses."

In my opinion, Dahl used this title in somewhat of an ironic way.  Usually, when we speak of a lamb to the slaughter, the lamb is some innocent thing that is being led off to be killed.  In this story, however, the innocent thing (Mary) is actually the one who slaughters someone else.  I see some irony in this.

At the start of the story, Mary is portrayed as very meek and subservient.  She is something of a lamb in contrast to her husband who seems more assertive.  But then Mary seems to make a 180 degree turn.  Instead of being a passive lamb being led to the slaughter, she becomes an assertive being who is going to slaughter someone else.

So I think that the title is used ironically to make us think about Mary's change in personality over the course of the story.

Roald Dahl's "Lamb to the Slaughter" begins in the Mahoney home.  It is not clear as to which room in the house, but I picture it like a stereotypical sitting room (living room).  Mary is pregnant, so she is probably sitting in a big comfortable chair in order to do her sewing. For sure the room that the story begins in is located close to the front of the house.  The reason for that is because Mary hears the sound of Patrick's car tires on the ground and the shutting of the car door.    

When the clock said ten minutes to five, she began to listen, and a few moments later, punctually as always, she heard the tires on the gravel outside, and the car door slamming, the footsteps passing the window, the key turning in the lock.

Once Patrick comes home, the story continues to take place in that room.  The text says that Mary returned to her chair and her sewing, while Patrick drank his adult beverage.  The two other main locations within the story are the kitchen and the grocery store.