The English text reads better than many translations from Japanese that I've encountered. The movie is fairly faithful to the book, while each has its advantages.

As is so often the case, the book lets the reader spend more time in the thoughts of Aoyama, the main character. It also fleshes out his world and makes his son a much more important character.

The movie strengthens the character of Asami by keeping her main motivation but treating her back story with a lighter touch. It also ups the gruesomeness quotient.

The book is a quick read and worth your time if you admire the movie.

The first line is "'Why don't you find yourself a new wife, Pops?'".