Passage of the 18th Amendment suddenly provides a lucrative business for gangsters. High profits lead to fierce competition which the ruthless operators escalate into violence. The Thompson sub-machine gun, designed for but rejected by the military, is easily portable, extremely powerful and legal. This weapon in the hands of the gangsters escalates the violence to new heights. Inevitably, a few audacious, bloody murders, such as the St. Valentine's Day Massacre, garner nation-wide attention to the gangsters, particularly Al Capone.