Summer holidays have arrived - the weather is perfect and all the kids are playing outside. But where is Greg Heffley? Inside his house playing video games with the curtains closed. As he admits himself, he is an "indoor person" and is living the ultimate summer fantasy: a life without obligations, without rules. However, his mom has a different idea of what an ideal summer means... for her, it's nothing but a summer full of outdoor activities and with the whole family together. Which fantasy will ultimately win? Greg's or his mom's? Or will the new member of the Heffley family turn everything upside down?