Character Analysis
Capricorn has a number of men under his command—some from his own story-world, some from our world. Most of them are probably ruthless killers, hardened criminals, and general low-lifes. While they're pretty darn loyal to Capricorn, some things make them nervous.
Mo is one such thing (or person, as the case may be). When he's going to read aloud from Treasure Island, they "seemed to be feeling far from happy. They were looking at Mo with expressions of apprehension mingled with dislike […]. Perhaps one of them would vanish into the book through which Mo was leafing so undecidedly" (18.7). In their defense, they probably see people and things read into and out of books all the time, so their wariness of what might happen when Mo reads isn't unfounded.
Interestingly—and pretty satisfyingly too—when the Shadow turns on Capricorn, "none of his remaining men moved, none of the boys and none of the women came to his aid" (56.53). We might've expected the women, many of whom are unwilling captives, not to help Capricorn… but his own men? Really? So much for loyalty. Half of them disappear when Capricorn dies, and the rest run away.