Dear John starts in the present day with John watching Savannah from afar and thinking about how much he loves her and why their relationship dissolved. He then takes the reader back in time and narrates the story of their love.
There is, unfortunately, not much more to say about the book. Dear John has a pretty formulaic plot. Although Sparks is one of the first to set the age old boy meets girl love story in the modern, post-9/11 world, he does not delve into how the war affects the characters or go very deep in this area. In Dear John, it could be any war keeping them apart. This specific war is not important.
The interactions between John and his father create a nice sub-plot, and the descriptions of North Carolina were interesting to me, but that's probably just because I live in the state.
Overall, I would describe Dear John as light reading that is not painful to read but also not extremely enjoyable to read. If you need some beach reading, go ahead and borrow it. It will give you a few hours to escape, if nothing else.