During Prohibition, Chicago's Beer Wars turned the city into a battleground, secured its reputation as the gangster capital of the world, and laid the foundation for organized crime nationwide. Bootlegger bloodshed was greater there than anywhere else.

The machine-gun murders of seven men on the morning of February 14, 1929, by killers dressed as cops became the gangland "crime of the century." Or so the story went. Since then it has been featured in countless histories, biographies, movies, and television specials. The St. Valentine's Day Massacre, however, is the first book-length treatment of the subject, and it challenges the commonly held assumption that Al Capone ordered the slayings to gain supremacy in the Chicago underworld. Instead, authors William J. Helmer and Arthur J. Bilek assert the deed was a case of bad timing and poor judgment by a secret crew from St. Louis known to Capone's mostly Italian mob as the "American boys."

The target of the murder squad was indeed Bugs Moran, but the American boys, who were dressed as policemen and arrived in two bogus police cars, arrived at the garage where the massacre took place before Moran arrived. They didn't know who Moran was or what he looked like, and since none of Moran's crew would admit to being him, the counterfeit cops stupidly killed everyone, just to be sure they got him. Much of the evidence that pointed to the American boys was deftly and intentionally ignored by law-enforcement officials in Chicago. The story surfaced again briefly in 1935 with a manuscript written by the widow of one of the gunmen and with public knowledge of a lookout's long-suppressed confession. In the end, the machine-gun bullets heard 'round the world marked the beginning of the end for Al Capone.