Difficult but rewarding read

The narrator of the first half of the story is an academic in 2119 who is left in what remains of Britain after cataclysmic climate and political upheavals. He is researching a love poem written in 2014 that is now lost. This is Ian McEwan as his most obscure - it is difficult as well as uncomfortable reading. The second half is much easier. Here the narrator is the women the poem was written for and is set back in our current times. Here he brings all the confusing threads of the narrative together to a convincing conclusion. 'What we can know' highlights what we cannot know.