Fiction by Rachel Joyce.
Harold Fry is a man who sets out to mail a letter, and then decides to deliver it in person, walking across England to do so. The reason he does such an odd --and unlikely-- thing is the point of this story.
This was a pleasant book to read, not exciting per se, but definitely engaging.
As a side note, I liked the original cover art, with the rolling green hills, better than the current one above.
(alternate cover art image from goodreads.com)