A week later, Angela climbed out of a cab in front of her three-story walk-up in a tree-lined neighborhood in Boston. It felt good to be home. The late spring air smelled sweet and fragrant from the saucer-sized magnolia blossoms bursting on the trees in the courtyard.

"You're back," an excited voice called to her as she climbed the front steps of the building. She turned to find her neighbor, Esther, standing on the grass with her dog, Gordon. She was an older woman, around Angela's ...