The story is told to us by Raymond. We are introduced to Raymond when he and his family is having dinner, and through the dialogue between Raymond and his parents we get an impression of what kind of boy Ray is. He is not as polite as his parents (and perhaps other adults) would like him to be, and he’s not very concerned about it either. It is through Raymonds thoughts we first get to know Zachary (Zock) and what he looks like :
" Zock was ugly. His eyes were terrible even then; he had black, kinky hair and obviously must have worn braces every day when he was younger..."

We also get more input on Zack’s character, as far as his behaviour is concerned, from Ray’s thoughts. The story is written in first person.
The author also lets the characters’ actions show us their characteristics, for instance when the boys run off to Chicago and get a lift with a man that starts acting suspicious.. It does not exactly say in print that Zock is smarter than Ray, but Zock’s reaction tells us that he is more aware about danger and situations that could develop into something that none of them would enjoy. Ray, on the other hand, does not quite get it when Zock makes an indirect escape from the weird driver of the car:

"You got him mad," I (Ray) said. "What for?"
"A whim," Zock answered, feeling my arm. "Very strong for a blond boy," he laughed. "My, my, my."
"Why did you get him mad?"
"I’ll tell you all about it when you’re older," he said...
Zock comes across as an intelligent, young man, who basically knows what to say and when to say it. He cares a lot about Ray, even when he doesn’t get much in return. He has some experience on taking care of himself (he has been away from home before) and is somewhat poetical in stating his views on life, as we get an impression of after Ray and Zock has seen the movie Gunga Din three times in a row:
"It’s a shame he had to die," I (Ray) said. "Gunga Din. I wish he’d lived longer."
"It doesn’t matter," Zock said, very soft. ..."Nothing matters when you know it all. All the answers."

He also goes to Harvard, where he is a brilliant student and gets a girlfriend; Bunny. The choices he makes proves that he cares about the consequences of his own actions, apart from the fatal choice where he lets Raymond drink and drive.

Raymond is unstable, sensitive and impulsive. He lives in the moment and is a poor student. Zock accuses him of being melodramatic, an assertion I think is true. He starts drinking heavy when he is dumped by Annabelle, a cruel girl that he loves, and even though he claims that he can stop drinking he says that there is nothing else for him to do, than drink. So he hasn’t got much willpower.

The two main characters, Zock and Ray, are slightly built upon there being one "good" and one "bad" character. The author manages to give them both positive and negative qualities, Zock is clever and caring but also somewhat kind to a fault, and Ray is eventually apathetic but also feels guilt when he crashes the car and kills Zock. This is very important in a story to make it believable, it is rare (if not impossible) for a person to be impartially bad or impartially good.