Residential motels have long been places of last resort for many vulnerable Americans--released prisoners, people with disabilities or mental illness, struggling addicts, the recently homeless, and the working poor. Cast aside by their families and mainstream society, they survive in squalid, unsafe, and demeaning circumstances that few of us can imagine.

For a year, the sociologist Christopher P. Dum lived in the Boardwalk Motel to better understand its residents and the varied paths that brought them there. He witnessed moments of violence and conflict, as well as those of care and...