Crew: Although Book's perfectly happy as a wandering preacher, if he's to settle, he'll look for the familiar. People and roles that he's familiar with will make him far more comfortable, wherever he ends up. Gwen Cooper (torchwoodsheart), multiple openings.
The Flock: The people Book looks out for, the ones who turn to him for guidance. He'll be strong for them, no matter how much doubt he feels. Multiple openings.
The Operatives: Very few evil men believe that they are evil. That makes them all the more dangerous. Book knows the enemy -- he's been the enemy. And he'd rather steer clear of these people at all costs. They remind him too much of what he used to be, and have an unnerving habit of making that side of him necessary. John Thane (john_thane), Captain John Hart (lovesxbitch), multiple openings.