"Patriots Day" follows Revolutionary War re-enactors as they prepare to re-fire those shots heard 'round the world on April 19, 1775, in Lexington and Concord. Filmmaker Marian Marzynski's style is low key and at times whimsical (real redcoats didn't use cell phones), but the "living historians" are serious. Says one: "It is important to understand the passion of what took place here."