To go beyond the call of duty—that depends on how you define “duty.” Consider this thought experiment: you see people drowning and can save either a relative or two strangers. What do you do? For most, the first impulse is to save the relative, but the utilitarian view would dictate helping the strangers; why save only one person when you can do twice as much good by saving two? Most of the issues of Strangers Drowning (Penguin Press, $27.95) spiral out from this scenario. Is altruism a matter of emotion or of logic? Is rescue the same as saving? Are humanitarian NGOs just colonialism in another guise? And when have you done enough, if suffering continues? In detailed and compelling narratives that make the moral questions immediate, Larissa MacFarquhar profiles people variously called saints, heroes, or obsessive-compulsives. A couple feels their calling is to save unwanted children—and end up with a family of twenty-two. Driven to eliminate as much sheer suffering as possible, a man advocates on behalf of the millions of agri-business chickens. Another couple, realizing that a few dollars buys a mosquito net, gradually donates every expendable dime to charities, equating buying a soda for themselves to committing a murder. The size of donations, of course, depends on the donor’s income—a woman deliberates whether it’s moral to stay in a low-paying position she loves, if a more lucrative career allows her to give away more money. And if these “do-gooders” never really change the world, does that negate the improvements they make, or render “selfish” the satisfaction—even the exhilaration—they feel in trying?