The Summer I Saved the World in 65 Days by Michele Weber Hurwitz

Nina is enjoying the start to her summer, soaking up the sun. She watches her neighbor trying to plant flowers with a broken leg and gets the idea to do something different. She sneaks over later and plants the flowers and then decides to do nice things for others every day for the rest of the summer. She does it secretly, and it seems like a good idea, but another neighbor is worried someone is vandalizing their homes. Also, Nina's best friend likes a boy across the street, but Nina quietly likes him too. Nina doesn't know who she can talk to. Her parents are too busy with work, her brother keeps sneaking off, and she doesn't really have any other good friends. She misses her grandmother, and she's not certain her secret kindness is doing any good.

There aren't many books being written about characters doing nice things for others, so this book is a pleasant change. Nina and her best friend are an interesting contrast in characters. The friend is very self-centered, and Nina is trying to find ways to make others happy. The boy across the street is going through a rough time and questions Nina's efforts. His little brother and the lady next door add smiles to the plot.