Copenhagen centers on a meeting between the German physicist Werner Heisenberg and his Danish mentor, Niels Bohr, in German-occupied Copenhagen in 1941. The details of the meeting are one of the great mysteries of twentieth century science. Both physicists were engaged in solving the mystery of the atom and aware of the lethal implications of their work. Friends as well as colleagues, neither denied the meeting took place; neither, however, would agree "for the record" what exactly was said.

Michael Frayn makes Bohr's and Heisenberg's debate accessible for audiences by presenting the physics in "...plain language" for the benefit of Bohr's wife, Margrethe. Their discussion draws together politics and philosophy of both men, as well as their personal perceptions of reality, physics, and mathematics.