The most original aspect of this story has to do with the murder weapon. The perpetrator, Mary Maloney, gets away with her crime of passion mainly because she kills her husband with a frozen leg of lamb and then cooks it and gets the detectives to eat the very murder weapon they are searching for. The most important quote is in the following paragraph:
"It's the old story," he [one of the detectives] said, "Get the weapon and you've got the man." Later, one of the det4ctives came up and sat beside her. Did she know, he asked, of anything in the house that could've been used as the weapon? Would she mind having a look around to see if anything was missing - a very big spanner, for example, or a heavy metal vase.
It would never have occurred to the detectives that Patrick Maloney could have been murdered by being hit over the head with a frozen leg of lamb, especially after they have checked his wife's alibi and dismissed her as a suspect. The fact that her husband was a detective helps to mislead his fellow detectives. They assume that some criminal was taking revenge or something along those lines. If they had found the leg of lamb still in its frozen state, that might have prompted them to consider it more carefully, and they might have found some blood on it and an indentation in the meat where it had struck Patrick on the head. That was why Mary made haste to put it in the oven. Being the wife of a man who had a long career as a policeman had taught her a great deal about the way policemen think.