Its landscaped ground, chosen by Frederick Law Olmsted and dotted with Tudor mansions, could belong to a New England prep school. There are no fences, no guards, no locked gates. But McLean Hospital is a mental institution-one of the most famous, most elite, and once most luxurious in America. McLean "alumni" include Olmsted himself, Robert Lowell, Sylvia Plath, James Taylor and Ray Charles, as well as (more secretly) other notables from among the...