At the beginning of the story Sargent Major Morris comes to the whites home to tell them stories of when he was at India. In one of his stories he goes on to tell about a monkeys paw that was blessed by the magic of a fakir. He attempts to burn it but Mr.White insisted that he would take it even after being warned of the evil the thing holds.
After Sargent Major Morris leaves the house with many warnings to the family Mr.White tries and decide what he wants to wish for. With enough time and some thought processing he decides to wish for 300 pounds. When nothing happens the family doubts that it works and goes to bed.
So Mr.White and Mrs.White learn that the wish comes true but with a catch. What happens is that the Whites are outside drinking some tea and a man comes to break some bad news. With the news hitting that Herbert has died the man says that the company rejects all responsibility for his death but they do give them some compensation....300 pounds
With Mrs.Whtie upset she forces Mr.White 10 days after Herbert’s death to wish for him alive. Mr.White is not keen on this idea but Mrs.White forces him. With some time passing after the wish they hear a knock. Mr.White insists that they don’t open the door scared to know what his mutilated son will look like or what he’ll act like.
As Mrs.White scrambles to unlock the door to let in there dead son Mr.White in a panic races to the monkeys paw and wishes his son would stay dead. Know with both of them upset they go back inside and live life until his wife eventually dies of her grief
I think that the superstition is that no man can change his fate without the repercussions of whats to come when fate catches up to you.