Diary of a Wimpy Kid: Dog Days is a novel written by American author and cartoonist Jeff Kinney, and is the fourth book in the Diary of a Wimpy Kid series.It was released on October 12, 2009, in the USA and October 13, 2009, in Canada. The film, Diary of a Wimpy Kid: Dog Days, released on August 3, 2012, was based on the book and its predecessor, The Last Straw. It follows the narrator, Greg Heffley, on his summer break between seventh and eighth-grade.