From West Side Story in 1957 to Road Show in 2008, the musicals of Stephen Sondheim (1930-2021) and his collaborators have challenged the conventions of American musical theater and expanded the possibilities of what musical plays can do, how they work, and what they mean. Sondheim's brilliant array of work, including such musicals as Company, Follies, Sweeney Todd, Sunday in the Park with George, and Into...