When a director has to explain something to the audience, you know that something’s gone wrong. Thus was the case in Copenhagen, a play that dazzled brightly for its first act, culminating in a scene so profound that it was assumed to be the finale. The truth was sharply realised when the director took to the stage to explain that this moment of finality was simply the break for the interval – which I spent pondering what exactly the play could add with an extra act.

It transpired that these concerns were warranted, leaving the second act feeling like an unneeded epilogue. This is a terrible shame, as the first was utterly superb. Copenhagen explores a single event: a meeting in 1941 between physicists Neil Bohr and Werner Heisenberg. The two are on opposing sides of the war, and Heisenberg’s homeland has occupied Bohr’s native Denmark. Both work in the theoretical area of their field, and inevitably the play’s central quandary is atomic weapons.

Frequent asides are made during the events’ recreation, breaking the fourth wall and allowing detailed interrogation of even the smallest gestures. This device would not have worked without Archie Thomson’s wonderful direction, which has characters talking towards each other, but not to each other – monologues to the audience that allow us to peer at characters’ emotional struggles. Despite being riddled with heavy science, the play engages and turns the historical story into a thrilling, human, tale. Credit is due to the brilliant acting – in a play that relies entirely on lengthy dialogue, all three cast members handle it confidently (especially Rupert Stonehill, who portrays the moral dilemma of being a German scientist with a captivating intensity).

Unfortunately, the fantastic story does not carry through to the second act, which focusses too much on unneeded, and thematically irrelevant, science-y exposition (this may be because of my limited knowledge of quantum physics, but this is a position the majority of the audience will be in). There are callbacks to earlier conversations and meagre attempts to cleverly tease out metaphors from the physics – these do not work.

But this is a criticism of the play itself rather than Sunscreen’s production. Their staging is, for the most part, strong, though the Pilch’s shortcomings of being too hot and inexplicably noisy prove annoying. The design is beautiful; a white grid that expands across the floor and up the back wall in a mesmerising pattern, with a cosy living room to ground it. This is the best part of the play’s technical aspects, which are otherwise fairly weak – Jennifer Hurd’s lighting design is amateurish, attempting to draw distinctions between 1941 and the abstract ‘present’ by over-the-top colour changes which shatter immersion and make the production feel student-y. Similarly, music sounds tinny and never fills the room – a small fault, but one that takes you out of a story that is so elegantly crafted.

Copenhagen is a very good production, and a strong opening for the Pilch this year. It is let down by a script that ends on a weak note, and technical decisions that would have been easy to fix. But, on the whole, it is a very fine display of acting in a story that, for the first act at least, is quite magnificent.