Like a riddle wrapped inside a mystery inside an enigma, Werner Heisenberg's visit to Copenhagen continues to baffle scientists, historians and men of letters, decades after it took place.
Exactly why did Germany's top nuclear physicist meet with his half-Jewish mentor, at considerable personal risk, in September 1941? Was Heisenberg trying to persuade Niels Bohr, (subsequently the linchpin of the Manhattan Project) of the need to unilaterally abandon the bomb programme? Was he looking for a clue that would allow the Nazis to build the deadly weapon first? Or was there some other purpose to his mission?
These are the central questions that drive the plot of Michael Frayn's> award-winning play, Copenhagen, and which form the basis of hypotheses for three long-dead characters (the two physicists, plus Bohr's wife and secretary Margrethe).
I'm not giving too much away by telling you that this mystery is never really solved conclusively. There is a certain irony in this outcome: these finely honed minds can decipher the mysteries of the atom, yet flounder when it comes to understanding why one man should want to meet another.
It has to be said that Copenhagen does require you to focus the mind initially - the tale is set in the world of nuclear physics after all - but because Frayn's dialogue is witty and the technical details entertaining, you're soon absorbed into the plot and flattered into believing you know more about this highbrow science than you really do.
In this respect, there are some obvious comparisons with Tom Stoppard's cerebral hit of last year, The Invention of Love. Like Stoppard's classicists, Frayn's physicists use highly referential dialogue in their discursive retrospectives from the spirit world.
Copenhagen is not dissimilar, too, in the way it puts relationships under a microscope. Indeed, Michael Blakemore's direction (and Peter J Davison's circular set) reveal the trio of Matthew Marsh's Heisenberg, David Burke's Bohr and Sara Kestelman's Margrethe as elements of an atom: Bohr's wife as a calming, questioning nucleus, the two physicists as electrons, at turns avoiding and colliding with each other.
Another interesting touch is the thirty galleried seats for audience members that appear in a curve at the rear of the stage. This not only turns the Duchess into a theatre-in-the-round, but makes the on-stage audience seem like courtroom jurors observing the trial of the sardonic genius Bohr, his ruthlessly competitive protege Heisenberg, and their terrible, destructive legacy.
This is an accessible, engrossing play, brimming with ideas, analogies and strong performances, which rightly deserves its transfer to the West End.