The Secret Book Club (Main Street #5‪)‬

Flora, Ruby, Olivia, and Nikki start their own summer book club when well-loved books start appearing on their doorsteps in the fifth of Ann Martin's wonderful Main Street books.Flora and Ruby are about to start their second summer in Camden Falls. An element of mystery is instantly added when someone -- the girls don't know who -- leaves copies of a very special book on their doorstop, with instructions to read and discuss it. Olivia and Nikki also get books, and soon the girls are starting their own book club -- with some very interesting ties between the books they're reading and the things they're facing over the summer. But who's their literary benefactor? The girls don't need to read Nancy Drew to track down the answer....