In his absence, the two boys and their sister (who tells the story in the first person ) are decamped from London to live in a couple of rooms in a farmhouse on the Welsh Border. They help out on the farm and in exchange get fresh eggs amongst other things, and learn country ways, and start to grow up. The older brother James, is brilliant at maths but dyslexic with words (it does not use that word but you quickly realise how he is), Charlie, who brings the baby squirrel home is the youngest, the cheekiest, the naughtiest, but the one who loves Henry the most. They all learn about country practices, animals, birth and death, injury and much more. A good all round education for them and the reader too.
I know the age range is quoted for 7-11, but I read it and thoroughly enjoyed it. I recently read and reviewed here The Peppermint Pig by the same author - different entirely but a lovely style. With only 160 pages, a young reader will not get bored, and I think will get much pleasure from Henry's antics.