Two sweaty European dudes are driving around Patchogue, NY in July of 1939, asking around for Dr. Moore's cottage. When they don't have any luck, they realize they might have the wrong town, and try Peconic, NY next.
The two sweaty European dudes are Eugene Wigner and Leo Szilard, Hungarian-born Jewish physicists who had fled Europe as Hitler rose to power. They are driving around trying to find Albert Einstein, who is on vacation, so that he can get President Roosevelt's attention regarding the possibility of a German atomic bomb.
They finally find Einstein and tell him about fission and the possibility of atomic bombs. He is immediately horrified at the prospect of Hitler getting his hands on such a weapon, and the three men immediately begin composing a letter to President Roosevelt.
Six weeks later, Germany launches its blitzkrieg on Warsaw, effectively taking Poland, and Britain and France declare war.
Four weeks after that, Alexander Sachs—an economist, friend of Szilard's, and former advisor to Roosevelt—hand delivers Einstein's letter to the President.
Einstein's letter urges the government to start working closely with physicists to explore the possibilities of building atomic bombs, especially because Germany has already started stockpiling uranium. Roosevelt agrees that this matter requires urgent action.