The Guncle by Steven Rowley
For a long time now when people online ask for a book that lifts your spirits, "The Guncle" comes up repeatedly. So I moved it up to the top of my list and am so glad I did.
It's a very touching story which is funny and charming while the thread underneath it all is how we deal with grief in different ways and the lasting impact of our loved ones and our decisions. I didn't want it to end, but also couldn't wait to see how it all resolved.