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. Challenging the commonly held assumption that Al Capone ordered the wholesale slayings to gain supremacy in the Chicago underworld, authors William J. Helmer and Arthur J. Bilek assert the crime 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, entered the garage where the massacre took place before Moran arrived. Not knowing who Moran was or what he looked like, the counterfeit cops stupidly killed everyone to make sure they got their man.

Based on a careful review of reliable evidence, a critical reading of news accounts of the time, a 1935 manuscript written by the widow of one of the gunmen, and a lookout's long-suppressed confession, The St. Valentine's Day Massacre is a fresh new look at the crime that captured the nation's imagination. In the end, the machine-gun bullets heard 'round the world marked the beginning of the end for Al Capone.