Then is not a post-apocalyptic survival story. The apocalyptic event, which is never fully explained, that led to London becoming a frozen wasteland sets the scene for the story, but this is far more a literary mystery than a story of survival.
The writing style itself is quite difficult to get used to - it's quite bleak and time shimmers between the past and the present from paragraph to paragraph - this is a book that I had to pay real attention to, otherwise I would have been constantly lost.
Isobel has survived the event, simply described only as an unseasonably hot day that after a flash of light turns the world cold, and is sheltering in an office building with a man, and three teenagers. Having lost her memory, and continuing to have some kind of amnesia, she initially has no recollection of the event, or even of what has occurred just hours before. She is not particularly likable as a character, mainly because she has no memories to form a personality, likes or dislikes, and as she cannot remember nor really even distinguish between dreams and reality, she has an almost ghost-like quality.
Other characters fade in and out as the story progresses, and the whole book has a very ethereal but disjointed feeling. The ending is particularly poignant, but this book has no real resolution, which almost makes it a little bit too clever for its own good. This is not a fun read, nor action-packed, but I did like the ghostly, discombobulated feel. Yep, I've been waiting years to use that word!