Oh, what a wonderful book!
Written by the author of 101 Dalmations, it came as a surprise to me that it was a perfect teen coming-of-age novel. What a gem!

It was written in 1949, and set slightly earlier.The Mortmain family ( Dad - previously successful author, now suffering from writer's block, his second wife Topaz - ex artists model, oldest daughter Rose - with great expectations, middle daughter Cassandra - heroine, and son Thomas - a schoolboy) all live in a crumbling Suffolk castle. Dad and Mum fell in love with it and bought it to house their three tiny children. Mum died, Dad fell into a decline and stopped earning, then took a second wife who helps them scrape a living. This is when the novel starts.
It is in effect the diary of Cassandra, who starts with the story of their poverty-striken life.As children, they don't really mind, and just get on with it.

As the novel progresses, rich Americans come to live next door, and puberty comes knocking. Love (or is it?) blossoms between various members of the cast, and it all weaves beautifully towards a shock ending. Fabulously weepie.
The writing is wonderful. Cassandra is cast as a budding writer, which explains her fluidity of style and adeptness at description. She talks about the family's ambivalent feelings towards the newcomers, Rose's desperate chasing after marriage to help them out of poverty, her father's struggle with writing, and her own first moves towards adult relationships.

Despite the fact that Dodie was long past her teenage years when she wrote it, it is fabulously accurate. The first time you feel an attraction to someone, your first kiss, feeling attracted to someone you know you shouldn't be and how you tell them, that dreadful embarassment about your family while still feeling fiercely protective. All these things are vividly recounted.
Cassandra also has a wit about her that is very attractive, and makes her a very likeable heroine. I wish I could tell you the end, but it would spoil it - you'll have to read it.