Until 1986 any man who, with romance on his mind, traveled with a woman other than his wife across the state lines of America could be guilty of a federal felony. Such was the legacy of the notorious Mann Act of 1910. Spawned by a national wave of "white slave trade" hysteria, the act was created by Congress as a weapon against forced prostitution.

It was so loosely worded that the Supreme Court soon extended its coverage: any man who intended to commit an "immoral act" with a woman who had crossed a state line, either with him or to visit him, could be prosecuted. In the 1920s, this sort of amorous behavior could send a man to prison for up to five years.

1. Crossing over the Line is the first history of the Mann Act's often bizarre career, from its passage to the amendment that finally laid it low. In David J. Langum's hands, the story of the act becomes an entertaining cautionary tale about the folly of legislating private morality.

Langum recounts the colorful details of numerous court cases to show how enforcement of the act mirrored changes in America's social attitudes. Federal prosecutors became masters in the selective use of the act: against political opponents of the government, like Charlie Chaplin; against individuals who eluded other criminal charges, like the Capone mobster "Machine Gun" Jack McGurn; and against black men, like singer Chuck Berry and boxer Jack Johnson, who dared to consort with white women.

The act engendered a thriving blackmail industry and was used by women like Frank Lloyd Wright's wife to extort favorable divorce settlements. The social costs exacted by the Mann Act, Langum argues, send a clear warning about the government's ability to wage "wars" against pornography, drugs, or art considered "obscene." Complete with archival photographs, Crossing over the Line will appeal to anyone interested in American history, popular culture, law enforcement, or the history of sexuality.