The Green Man was the first novel in which Amis began to express intimations of mortality. In Ending Up, he faced the topic of death head-on, more than in any of his other books. (By comparison The Old Devils, for example, is light reading.) When I first read it, over 30 years ago, I found it depressing enough, and it rings even truer now. As always with Amis, there is brilliant humour, but here it is unremittingly black.
The story describes the final stages of the lives of five old people, each connected with one or two of the others, but (in some cases reluctantly) forced to share an isolated country cottage through lack of money. It could be described as one of Amis' genre books, as the format is classical Greek tragedy. Aristotle's unities are more or less obeyed; all the action takes place in or around the cottage, and the only other characters are very much bit-parts.
Of the five ill-assorted characters, three are unselfish and likeable; a fourth, Marigold, is vain and selfish, but wins the reader's sympathy for her desperate attempts to "keep up appearances". The fifth, Bernard, is the villain; he is unable to control his distaste for a life he feels is wasted, and for the lifestyle now enforced on him. His only diversion is to take out his bile on the others, with his success depending on their strength of character. Adela, his long-suffering sister, and George, his bedridden, aphasic brother-in-law, are quite unable to fight his psychological bullying. Marigold is better able to resist Bernard's venom, but it has almost no impact on Shorty, who is - literally - the "eternal squaddie". (When Bernard was an Army officer, Shorty was his batman; they had a brief affair with each other, which is long since water under the bridge, but which caused Bernard to be cashiered.)
As the plot progresses, each character - even, at some stages, the disillusioned Bernard - intermittently tries in their own way to hang on, or even win back, self-respect. The exception is the irrepressible Shorty, who is more than happy with a modest ration of fags, whisky, etc. When Bernard, feeling that he has little else for live for, and realising that the others are starting to cope with his behaviour, finally escalates his campaign against them, the results are terminally disastrous.
This is possibly Amis' best book. For once, he manages to forget to be Kingsley Amis, and just writes.
However, probably one to avoid if you fear the prospect of getting old ...