Applejack is requested by HRH Princess Cadance, to travel north to the Crystal Empire in order to assist her and Shining Armor in cultivating the long lost crystal apple, a fruit imagined to have powerful healing properties, when grown properly. Unfortunately, the crystal ponies lack such farming skills, so who better than an Element who is also an experienced apple farmer?
This is a sequel to: Orange and Blue, I Do (Book 3)
There is a later sequel to this story: Cultivating Love (Book 5)