When M-G-M proposed a film about the development of the atom bomb and its inherent dangers, President Harry Truman provided the title himself, advising producer Samuel Marx to make a good picture and "tell the people of this nation that for them it is the beginning or the end." A gripping dramatization of real-life events, The Beginning or the End opens prior to World War II, when American scientists under the guidance of Dr. Enrico Fermi (Joseph Calleia) win the race to split the atom. Aided by a letter from Albert Einstein (Ludwig Stossel). physicist Matt Cochran (Tom Drake) and his colleagues convince President Roosevelt (Godfrey Tearle) to authorize the construction of a nuclear weapon. Assisted by Cochran and Colonel jeff Nixon (Robert Walker), General Leslie Groves (Brian Donlevy) is placed in charge of the Manhattan Project, a billion-dollar undertaking that will culminate in the bombing of Hiroshima and Nagasaki, and the end of WWII.