This book is pretty much what it says on the tin: an exploration of what life was like in a medieval castle, mostly drawing from the case of Chepstow Castle, but mentioning other castles when variations and other points needed to be made. It covers the life inside the castle — what the Lord and Lady of the castle would do, how they would entertain themselves — but also how the castle was supported by the lord’s people. There’s some space given to warfare and surviving siege conditions, as you’d expect, and the exact social circumstances that promoted the building and use of castles.
It’s an easy enough read, though there wasn’t much that surprised me in terms of being new information. For a more engaging read, I’d probably turn to Marc Morris’ book: Castles, which covers some similar ground. Probably makes a good reference read (no surprises there — the cover mentions that George R.R. Martin used it as such, which is probably why it and the other related books are having a nice little lease of life in bookshops)!