I haven't read the book, but, being an elementary school librarian, I read the version for upper elementary/middle school age....I kept substituting "Boomer" for "Marley" and it worked just fine! HA....I want to see the movie, but I don't know if I can or not.....It's like I live with the puppy version of Marley (Boomer) but I also live with the elderly Marley (Cassie).....I'm afraid we will be facing the same thing that Marley's owners had to face when he got older very soon with Cass dog....so I haven't decided if I'm going to see it or not right now......