If you are looking for a book that has stories about cats that ALL have happy endings, this is not it. This is a book that is filled with lots of short tales from around the globe (many in England, where this book is published) about actual cats and they range from happy, sad, bittersweet and everything in between.
There are heroic WW2 cats, cats who go on an incredible journeys, cats who survive unfortunate things, and a lot of rescues (cats and people).
There are stories about cats who were injured (by humans or otherwise), were born differently than other cats, and obviously as many of these take place in a past time, not all of them are alive now (and a few don't even make it past the end of the tale itself). If these things are not things you are comfortable with reading, or if you have just lost a pet, you may not be ready for this book.
There are some amazing tales about cats (and the people and other creatures that love them) in this book so be ready for quite the adventure when you read it.