Lucien Swinton
Lucien figures his role is to keep the peace between Peter Foster and Cassius as they plan out the particulars of the attempt. He keeps his voice low and tempered, and he's the one to suggest a somewhat public venue with many easy exits -- the steps of a theater, say.
He's concerned about the vampires getting tetchy, given the recent to-do over Steele, and will say so, and question Cassius regarding his strategy for keeping the vampires from thoroughly panicking in ways that are 'unhelpful'.
He'll also say that he'll do his best to keep the more 'extreme elements' in his own caucus from taking a cue from this as carte blanche to ignore the treaty.
He treats Peter with a stiff sort of formality, and oh so slightly bristles at Robert, but he's polite to both. He's clearly grateful for Bertie's presence, especially after seeing that Peter has brought a second.
He's frosty, but polite enough to Cassius, and deferential to Mac and Una both.