When you've watched the movie Minority Report twice...
... ask yourself when the absolutely worst moment comes for good people in this story. (There's a big flaw in this movie, in that the wife of Tom Cruise doesn't get introduced early enough. But once she is, you do see that she is a major character.)
This is like a book with two main characters, where ideally the action bounces back and forth between them both. That doesn't happen in this movie until very late. So, you see the flaw.
Any time a director or writer introduces an important character late, it's a flaw. Still, I like to use this movie not just to criticize it for this flaw.
Given this flaw, and given that in effect you have one major character at the beginning of the book doing all the major stuff, and then, towards two-thirds of the way through, you have another one taking over, the only way around the flaw is to consider them as part of one team, poorly delineated, but one team that you care about.
So that's the next part of your homework. Find out when the worst moment happens for the main character team.
I have to go to bed now. Good luck all of you. And keep on writing! Love you all.