When we first meet the Whites, they are basically happy people, though maybe a tad lonely and isolated. On a dark and stormy night, they get a visitor, Sergeant-Major Morris. He gets drunk, tells them about his adventures in foreign lands, and shows them a monkey's paw from India with the power to grant three wishes.
Morris warns the Whites that the paw was specifically designed to hurt the people who wish on it. He has wished on it himself but isn't sure if he would do it again. Since the paw couldn't possibly really have magical powers, what harm would there be in wishing on it, just for fun?
Well, Mr. White does make a wish, for two hundred pounds, the amount of money needed to pay off the family home. This proves to be a complication after the climax, which happens next. Now the Whites will never be sure whether what happens in the climax is a result of the wish or not. If the wish had never been made, it would probably be a little easier for them to deal with the climax.
The very next day, Herbert is killed in an accident at the factory where he works. To compensate the Whites for his death, Herbert's employers give them two hundred pounds, the exact amount Mr. White wished for.
When Mrs. White begs Mr. White to wish Herbert back to life, we're pretty sure he's going to do it. But when it seems that the mangled, undead Herbert is actually at the door, there's a lot of suspense over whether Mr. White will go against his wife and do what he wants. Ultimately his fear of undead Herbert wins over his fear of his wife.
This part is a little frustrating. Mr. White does wish, though we aren't told precisely what he wishes for. All we know is that the banging on the door stops. The implication is that Mr. White wished Herbert back to death.
In case you were thinking maybe somebody besides undead Herbert was at the door, the concluding lines suggest it was probably him. Remember, the Whites live in an isolated area and only have one neighbor. When they walk outside after the knocking stops, the area is completely quiet and empty....