‘Michael Frayn’s tremendous play is a piece of history, an intellectual thriller, a psychological investigation and a moral tribunal in full session’ Sunday Times ‘A profound and haunting meditation on the mysteries of human motivation’ Independent ‘Frayn has seized on a ral-life historical and scientific mystery. In 1941 the physicist Werner Heisenberg, who formulated the famous Uncertainty Principle about the movement of particles, and was at that time leading the Nazi’s nuclear programme, went to visit his old boss and mentor, Niels Bohr, in Copenhagen. What was the purpose of his visit to Nazi-occupied Denmark? What did the two old friends say to each other, particularly bearing in mind that Bohr was both half-Jewish and a Danish patriot?… Frayn argues that just as it is impossible to be certain of the precise location of an electron, so it is impossible to be certain about the workings of the human mind… What is certain is that Frayn makes ideas zing and sing in this play’ Daily Telegraph