It rains all the way through and I did not notice until my sister told me.

There are books you read and books that read you, and this one had my number by page thirty.

I will start with the rain because I have to. It rains at the start, it rains all through the retreat, it rains on the last page, and Catherine says early on that she is afraid of the rain because sometimes she sees herself dead in it. I didn't spot any of this. Not one bit of it. My sister, who did an English degree in the eighties and has never once let it go, pointed it out over Sunday lunch and I sat there with my fork halfway up like a man being shown a card trick from behind. Then I went home and read it again with my eyes open and the whole book turned round and looked at me.

The sentences are the thing. Short, plain, laid down one after another like bricks in a wall — and then every so often one of them opens a door in the wall and there is a whole field on the other side. Nobody has ever made the word "and" carry so much. It ought to be monotonous and instead it is hypnotic; it is the sound of a man refusing to make a fuss while everything he has is being taken off him.

The retreat from Caporetto is the finest thing in it and possibly the finest war writing I've come across anywhere. The column of lorries stuck in the mud, the rain again, the road that will not move, the battle police at the bridge shooting officers for the crime of having got separated from their men. Frederic going into the river is a baptism, obviously, and I did spot that one, thank you.

Where the book struggles, and I have argued myself into and out of this three times, is Catherine. There is something not quite alive about her devotion. She wants to stop being a separate person; she says so, more than once. Some of the dialogue in Switzerland made me wince, all that talk of you are my religion and there isn't any me any more, and I could not tell whether I was watching two people genuinely undone by love or a man writing out the woman he wished existed. The others at the pub split straight down the middle on it and it got heated. Deborah was very good on it, actually.

And then the last thirty pages arrive and none of that matters. The hospital. The corridor. The waiter and his sandwich. The bit about the ants on the burning log, which is an entire philosophy of the universe smuggled in as an anecdote about a campfire, and it broke me clean in half. And then the ending, that famous flat quiet last paragraph, a man walking back to his hotel in the rain.

I put it on the shelf and did not want to talk to anybody for the rest of the evening.

Nine, and it is only not a ten because of the Switzerland stretch, where the book takes a long slow breath, and I confess I skimmed the horse racing.