"Thank you." Lib tried to think of some more conversational note to end on. "It's always intrigued me," she said, letting her voice rise, "why you Sisters of Mercy are called walking nuns." "We walk out into the world, you see, Mrs. Wright. We take the usual vows of any order--poverty, chastity, obedience--but also a fourth, service." Lib had never heard the nun say so much before. "What kind of service?" Anna broke in: "To the sick, the poor, and the ignorant." "Well remembered, child," said the nun. "We vow to be of use." As"