There are many reasons this has been a bestseller. First of all, it’s a short book that is easy to read.
It also has an intriguing plot that tries to answer the question of what makes humans happy. The ancient Greek gods Apollo and Hermes meet in a bar in Toronto and make a bet to see if animals will be happy if they are given human cognition and language. They put a spell on fifteen dogs, giving them the ability to speak and think like humans. These dogs make their own packs, with hierarchies. They each have distinct personalities, like humans. They even create their own language, though they still have the basic instincts of dogs (i.e. sniffing each others’ butts). Apollo and Hermes observe how the dogs interact and progress to determine the winner of their bet.
As a dog lover, I really liked this book. Now this may be a bit of a spoiler, but not all of the dogs make it to the end of the book. Nevertheless it is an excellent book that you should definitely read!