This excellent revival - 11 years after an Auckland Theatre Company production - is stupendous intellectual stimulation, wonderfully presented and unapologetically wordy.
Like Tom Stoppard's tragi-comedy Arcadia, Michael Frayn's remarkable drama is a melange of physics, philosophy and history, brimming with ideas and the connections between them.
It centres on a real-life mystery: why did Werner Heisenberg - head of a German nuclear programme and Niels Bohr's erstwhile protege - visit Bohr and his wife, Margrethe, in Nazi-occupied Copenhagen in 1941?
As unreliable memory and anger throw up different answers and deeper questions, Frayn intriguingly delves into the social psychology of scientists, the ethics of the Bomb and mid-war life in central Europe. (Heisenberg says puddles of phosphorescence burning in Allied-bombed German cities are hard to keep off his shoes: "As if the streets have been fouled by the hounds of hell.")
Scientific explanations abound - atoms are snowflakes and fission bombs are avalanches - but Frayn is subtle enough not to let any metaphors solidify into heavy-handedness.
The three-hander is the New Zealand debut for the Northern Lights production company, English director Alex Bonham and London actor Simon Kane (as Heisenberg), and they all deliver with aplomb.
Kane especially shows mastery from the start, and both he and Bruce Phillips as Bohr live their challenging dense paragraphs, exchanging them with rapid-fire excitement and clear enunciation.
The script cleverly see-saws its sympathy between Bohr and Heisenberg, while Margrethe, played by Jennifer Ward-Lealand as a shrewd observer, is more cipher than character.
Rachael Walker's satisfying conceptual theatre-in-the-round design places all the action on a gigantic hydrogen atom, using three black stools as sub-atomic particles (the costuming suffered a little in comparison). A ring around the claustrophobic nucleus is lit up like a fire, but the "firewood" is books and shoes: the Holocaust and Hiroshima press into the conversation.
Concentration is richly rewarded; have a coffee before you go. Recommended.
Copenhagen is on at Tapac, Western Springs, until June 10.