The spirits of Werner Heisenberg, Niels Bohr and Bohr's wife Margrethe, meet after their deaths to attempt to answer the question that Margrethe poses in the first line of the play, "Why did he [Heisenberg] come to Copenhagen?” They spend the remainder of the two-act drama presenting, debating and rejecting theories that may answer that question.
Heisenberg – "No one understands my trip to Copenhagen. Time and time again I’ve explained it. To Bohr himself, and Margrethe. To interrogators and intelligence officers, to journalists and historians. The more I've explained, the deeper the uncertainty has become. Well, I shall be happy to make one more attempt."
Along the way, Heisenberg and Bohr "draft" several versions of their 1941 exchange, arguing about the ramifications of each potential version of their meeting and the motives behind it. They discuss the idea of nuclear power and its control, the rationale behind building or not building an atomic bomb, the uncertainty of the past and the inevitability of the future as embodiments of themselves acting as particles drifting through the atom that is Copenhagen.