How is a totalitarian state like a love affair? They both leave archives behind when they go. How is a totalitarian state like a bad love affair? The archive that survives the end of each is a monument to abuse, surveillance and betrayal.

This equivalence is indirectly evoked in the opening pages of Jenny Erpenbeck’s fourth novel, Kairos. The totalitarian state in question is the German Democratic Republic, whose Ministry for State Security (or Stasi) generated, in its forty years of existence, ‘the equivalent of all records in German history since the middle ages’ (this factoid comes courtesy not of Erpenbeck but of Anna Funder’s semi-elegiac 2003 portrait of GDR life, Stasiland).

The love affair at the centre of Kairos is that of Hans and Katharina. When it begins, Hans is in his fifties, is married and has a son. Katharina is nineteen. They meet on a bus in East Berlin in July 1986. Their affair, it spoils nothing to say, unravels at the same time as the GDR itself.

Kairos begins in the present day. Katharina, now married herself, receives news of Hans’s death, along with a tranche of his papers. It prompts her to turn to her own archive – a suitcase ‘full of letters, carbons, and souvenirs, “flat product” for the most part, as the archivists like to say … A long time ago, the papers in his boxes and those in her suitcase were speaking to each other. Now they’re both speaking to time.’ That comes in the prologue. An epilogue sees Katharina delving into another archive, neither her own nor Hans’s this time, but one in which she finds a previously hidden truth about their love. How is a love affair like a totalitarian state?

Kairos is a fearsomely symmetrical novel. Between archival prologue and archival epilogue are two long sections, ‘Box I’ and ‘Box II’, separated by an ‘Intermezzo’ lasting less than half a page. The word ‘Intermezzo’ suggests the novel’s other structuring principle, which is music. More specifically, the book is shaped to mimic the material devices on which music is stored, or was stored in the 1980s: vinyl records and magnetic tapes, each of which has a side A and a side B. Where art meets the archive, where the personal meets the political: this is Erpenbeck’s typical thematic territory. It’s her literal territory too: she was born in the East Berlin district of Pankow in 1967 and reached adulthood as the GDR was in its final years.

Describing the plot of Kairos to friends, I found myself half-apologising for it. It is, after all, about a middle-aged writer having an affair with a much younger woman, and as soon as I said this, I saw eyes glazing over, interest rapidly waning. What I should have started with was not the standard-issue plot but the impressively non-standard ways in which the novel embroils you near-simultaneously in two points of view. It’s a novel that comes as close as fiction can allow to representing the shared or double consciousness that arises when we fall in love. Erpenbeck uses the same techniques to represent the sundering of that double consciousness (this is where the sense of symmetry feels most acute).

Erpenbeck shuttles back and forth between Hans’s and Katharina’s points of view, often within the same paragraph and often without signalling that the move has occurred. She generates from these movements and from the fleeting insights of an omniscient narrator the sense of two minds ‘speaking to each other’. After Hans and Katharina first have sex, ‘It will never be like this again, thinks Hans. It will always be this way, thinks Katharina. Then sleep puts an end to all thinking, and what happened to them both today is inscribed permanently – while they lie together, breathing peacefully – on each one’s cerebral cortex.’

The prose, in Michael Hofmann’s smooth translation, is plain. The observing eye is minutely perceptive. The effect is profoundly involving. As with certain albums, side B is related to, but tonally distinct from, side A. The first half of the novel is lushly romantic, even saccharine. ‘It’s bliss,’ Hans tells Katharina, as they have lunch. They share music with one another: Mozart, Bach, Schubert (on vinyl records, of course). The second half – following an act of betrayal – turns sour, defeatist and claustrophobic. The betrayal is Katharina’s: she sleeps with Vadim, a young colleague in the theatre where she works. Hans, formerly worshipful, turns emotionally abusive; he subjects her to audio tapes on which he berates her for her failings (naturally, each tape has a side A and a side B).

The second half of the novel throws shadows back across the first. What seemed romantic now appears worryingly obsessive; what felt like bliss now seems closer to coercion, or paranoia (in the restaurant, just before he tells Katharina that their relationship is bliss, Hans notes the ‘Stasi expression’ of the waiter). And what begins as a novel about a passionate affair and its archival remains turns, both neatly and painfully, into a novel about failure: the failure of love, the failure of political hope, the failure of the once-omnipresent East German state. The title – not a German word but a Greek one – isn’t to be trusted. Early on, Erpenbeck is careful to tell us that Kairos is ‘the god of fortunate moments’. She knows that every fortunate moment is the obverse of an unfortunate one. Every album has a B side.