Time Bomb: The race between two geniuses to create the one weapon that will decide World War II, by Malcolm C. MacPherson, 1986
Enrico Fermi and Werner Heisenberg, proteges of Nils Bohr, both won Noble Prizes in physics when young men. Fermi fled to USA, Heisenberg stayed in Nazi Germany.
Really good book. Reads like a suspense story. Available used on Amazon.