After a hard day of work, you return home and open your mailbox. All is usual, but you soon find another letter with an unknown sender. You carefully open the letter to keep the contents as it is. The message reads:
When you have received this letter, go to the library. If you search hard enough, it will lead you to the answer. Enter through the back door. Make sure to enter quietly, careful not to wake the (unexpectedly sleeping) guard dogs. Once you have found the book we are looking for, tiptoe to the side exit. Give us the book you have found and have in your hands to receive your reward.
PS: Lemons are sour treats. ~~~ Water on rock/dirt.
The letter comes with an image, which you assume is unrelated to the message. Somehow, you think it could play a big role later on. The image is attached below:
As read in the letter, what is the "genre" of the book you are looking for?
Personally, I would start decoding the letter.