The play takes as its starting point a historic event--the visit made by the German physicist, Werner Heisenberg, to Neils Bohr during World War Two in 1941. The two physicists, who had collaborated for so long on the development of quantum theory, were now on opposite sides. Bohr was half-Jewish and a citizen of occupied Denmark. Heisenberg was a professor at Leipzig in Germany, but unknown to Bohr, he had become head of the Nazi regime's project to harness atomic energy. Both men were under surveillance. The play explores a number of issues: the possible motives for this visit, whether it could have taken a different course, and if so, whether this might have produced a different outcome to the World War, since it is known that Heisenberg broached the subject of the work being done to produce an atomic bomb. This raises the further issue of the morality of scientists working on atomic energy, which had the capability to produce a new weapon of incredible destructive power.