I have a new idea for a novel turning about in my head. It would center around a theatre production of a musical, though would really be about the interactions between some of the participants. I was thinking of a play by Sondheim in particular. I wouldn't make fun of the play; I like it, and would represent it in a flattering light. There would be rampant use of character names and lines and lyrics. I'd mention Sondheim by name; there would be no question that he wrote it, not me. So, do I need permission to use it, or is it decidedly "fair use" to do something like this? If I do need permission, who do I ask? Would I have to pay for it?
If I have to pay, then really, I'm just going to scrap the whole idea.