Dan Marshall, the author of this memoir, loves to swear. ‘It’s very difficult for me to write a sentence without using a bad word,’ he tells us. ‘That last sentence, for instance, was fucking impossible for me to write.’

Dan is young, rich and American. One day, in his twenties, he and his girlfriend, Abby, were on holiday, lying poolside at the Marriott resort in Desert Springs, California. He is in a world of material and sexual abundance. ‘My siblings and I were lucky, living with the proverbial silver spoon jammed firmly up our asses,’ he tells us. He has lots of sex. So does his gay brother Greg. His mother’s cancer was ‘under control’. As for his father, ‘He’d start every day with a cup of coffee and a dump, and end it with a glass of wine. He was living the dream.’

But the dream becomes a nightmare. Dan leaves the pool to check his phone. There are nine missed calls from his family. Desperately bad news: his father, Bob, has been diagnosed with ALS (Amyotrophic lateral sclerosis), or Motor Neurone Disease. In America, it’s known as Lou Gehrig’s disease, after the baseball player who died of it. The prognosis is terrible. ALS attacks the communication system between the brain and the rest of the body. It’s what Stephen Hawking has. But unlike Hawking, most people don’t live a long time. ‘In other words,’ says Marshall, ‘Lou Gehrig’s disease is a real ugly motherfucker and is pretty much a death sentence.’

The rest of this book, which is being made into a Hollywood movie, shows what happens when an affluent, materialistic American family faces an appalling crisis. It’s sort of like Dave Eggers’s A Heartbreaking Work of Staggering Genius, in that it’s about a guy whose mother has cancer, but then his father beats her to the grave. But Marshall is always telling us what a slob he is. ‘Dan, you’re a fucking idiot, you fucking fat fuck. I felt fat as shit.’

Marshall wants to show us a certain class of rich people (the type of American family who have a big house, a maid, a Lexus, and so on) and how they cope in extremis. Of course, they do what anybody else would do. They swear, they yell, they argue. They tell jokes in bad taste — really shockingly bad taste. Marshall’s great talent is to take all the swearing and sick humour and somehow make it moving. And it’s extremely moving. As the book goes along, towards Bob’s inevitable death, Dan jerks us into fits of guilty laughter — and also, simultaneously, swells our tear ducts.

He notices that his parents are ‘holding hands and kissing all the time. It was sort of disgusting, really — a couple of dying fucks making out and shit.’ His mother wants him to move back to the family home. She keeps texting him. ‘I wanted to kick whoever taught her how to text in the teeth,’ he tells us. Then he does come home. He puts his life on hold. He becomes a carer.

Bob’s disease rages through him. Dan’s bad-taste humour runs in parallel, until it reaches a kind of fever pitch. When Bob needs an automatic speaking device, like Stephen Hawking’s, Dan programmes it with, among other things, the words, ‘Boy, I could use a blow job.’ Then Dan’s mum (whose cancer has come back) says that maybe she will give her husband a blow job. Worrying about this potential event, Dan has this exchange with his father:

‘That’s cool. I just hope I never walk in on that’, I said…

‘DANNY,’ my dad managed to say in as angry a tone as he could muster. ‘Let’s not be so disgusting all the time.’

Dan drinks, and stuffs his face, but he moves towards a sort of enlightenment. At one point, he has ecstasy-fuelled sex. ‘Okay, put your dicks away. Let’s not get too pornographic here. Just kidding. Let’s do,’ he writes.

Towards the end, Bob decides he wants his breathing apparatus turned off, and sets a date. At this point, I put the book down; part of me couldn’t bear to go on. The end is really sad. If I had to give a short description of this book, I’d say that it’s crude, obscene, haunting, and very good.