Alt-text: "I honestly can't decide wether Halen in the last panel is him being genuinely delighted, just trying to be polite or a rare instance of sarcasm. You decide."
Traditionally as a guild member you'd just call the leader of a guild hall "Master", as Kat and Halen are doing with Peck. As an outsider, though, Book isn't so sure about that, so he refers to Halen as "Master", too, since he's basically the second in command in Serpent's End (who would have thought? :O ).
Relettering is at page 120, and has thus entered chapter three (and is almost halfway done - hype!).