Someone is killing San Francisco's homeless at the rate of one a week. When one of them, a man Dr. Andrew MacCrimmon has befriended, is killed, he says enough is enough. Having nothing to lose-his wife, Karen, has left him to live with a lawyer-he goes on the streets himself as a homeless man to lure in the killers. After weeks of boredom, humiliation, and physical discomfort he succeeds-with fatal consequences.