A review and summary of 11/22/63

WARNING: SPOILERS
I have just finished the book 11/22/63 by Stephen King.  I enjoyed the book very much, it kept me intrigued and I wanted to keep reading.  I would only give it 8.5 out 10 because for about the second quarter of the book, I was getting bored.  Nothing happened for that quarter of the book and I did not always want to read it.  The book got better though and I was interested again, so most of the book was good.  This is why I gave the book an 8.5/10.
In the book, Jake Epping is a teacher in Maine in 2011.  His friend Al, who owns a diner calls Jake and tells him to come to the diner one night. When Jake sees Al, Al is dying of cancer, which is strange because a day before, Jake saw Al and he was completely healthy.  Al shows Jake a portal to the past that he found in his diner.  He explains that the portal takes him to 1958, and no matter how long he is gone in the past, when he comes back, it has been two minutes in the present.  Also, every trip to the past resets in 1958.  Al tells Jake that he was in the past for 5 years, trying to stop Lee Harvey Oswald from killing John F. Kennedy, but his cancer prevented him from finishing the job.  He wants Jake to go back to the past for five years and stop Lee Harvey Oswald.  Because Jake is recently divorced and he doesn't see many good things for himself in the future, he accepts.  There is another thing Jake must do before saving the president.  He taught adult high school lessons over the summer for people who never graduated, and he teaches a man named Harry Dunning.  Harry was beaten with a sledgehammer as a child in 1958 by his father and barely survived while the other members of his family were killed.  Jake needs to know that what he does in the past can have an impact on the future, so he goes to the past to stop Harry's dad from killing his family and damaging Harry's brain.  He goes through a journey to stop Harry's father, and eventually shows up at the house on the night Harry's dad killed his family and saved all but one of the Dunning family besides the father.  Jake comes back to the present and tells Al what happened.  He sees that the picture of himself and Harry is no longer in his house, so he had succeeded in changing the past.  Al only remembers who Harry Dunning his because he was so close to the portal.  Jake says he will get some sleep and talk to Al in the morning before leaving for five years.  Jake goes to Al's house in the morning and finds that Al committed suicide.  Jake goes back to the past, stops Harry's father, this time from killing anyone, and goes to live in Florida.  In 1960, Jake moves to Texas and begins to plan to investigate Lee Harvey Oswald once he moves back to the United States from Russia.  Jake moves into a town south of Dallas called Jodie.  He lives there until the assassination and gets along well with the people who live there.  Jake falls in love with a woman in Jodie named Sadie.  George and Sadie spend a lot of time together and they decide to get married.  Jake even tells Sadie where he is really from and what he intends to do and Sadie believes him.  Jake is badly beaten soon before the assassination and he forgets a lot about what he has to do, but Sadie helps him remember it over time.  He doesn't want to involve Sadie anymore in his plans so that she doesn't get hurt, so he hides from her in Ft. Worth two days before the assassination.  Sadie finds Jake though, and she says he is to weak in his current state to do what he intended to do alone, so she comes with him.  The reach the 6th floor of the Texas School Book Depository just in time to stop Lee Oswald from killing the president, but Lee shoots and kills Sadie.  Lee is then shot by security from the street who heard a gun go off and saw him in the window with a rifle.  Jake returns to Maine and hears that there was a massive earthquake in Los Angeles that killed 7,000.  This didn't happen in his time.  He returns to the present and discovers the world to be much worse than it was before he saved John F. Kennedy.  This is not because John F. Kennedy turned out to be a bad president, but because the past is not supposed to be changed.  Earthquakes happened all over the world that had plummeted into nuclear war.  Scientists say that the world will be destroyed by the year 2080.  Jake knows what he has to do, so he goes back to 1958 to reset the past and then returns to 2011.  Everything was now just the same as it was before, and Jake continues his life in 2011, five years older than he was 2 minutes before.