Grant, the narrator, is a frustrated guy and that comes out in the tone of his narration. He's tired of trying, wishes he could run away, and his desperation comes out when he describes situations like this one:
I knew Miss Emma expected me to come back and tell her all about Jefferson, but I had not thought of a good lie yet. I couldn't go there and tell her what had really happened; that would have hurt too much. I couldn't go there and say that we had had a good talk; she probably wouldn't have believed it, not after the way he had acted when we were there together. I needed time to think, to think of something. (12.1)
This quote is complicated, and its complexity gives us a lot of information about the kind of community that Grant lives in. First of all, it has unwritten rules, and everybody knows them. Even though Grant doesn't really dig his role as maker-of-men, he still knows what Miss Emma expects of him… and he plans to do what he's expected to do.
We also find out that Grant has a heart (surprise, surprise!). He knows that what he witnessed in the jail cell with Jefferson would really hurt Miss Emma and he wants to protect her from that information, so has to think of something believable for her. Unfortunately for Grant, Miss Emma knows that Jefferson is in a pretty dark place, so there's no way he can come up with really good news for her. His lie has to be the right amount of sad to be believable mixed with something happy to give Miss Emma hope.
In these struggles over right thing to do Grant's tone suggests a pragmatic (and yeah, sure, kind of cynical) hope and affection for humanity. He may be kind of grumpy, but his heart isn't two sizes too small.