Brint. Not someone we'd want to sign on as our guide, but sure enough, that's the role he plays in the story. (We might peg him as an antagonist, too, except that he's not really a villain or an enemy; he's just not on Adam's side.) Brint even calls himself Adam's guide (4.1); again, self-definition can't be taken for truth, but it's an important part of characterization. This just goes to show you that a guide isn't necessarily always there to help. Sometimes he's there to throw really invasive questions in your face repeatedly until you retreat into a vegetative state.