Since becoming marefriends with Twilight, Princess Luna has been more cheerful, more cheerful than she has ever been. This brings about suspicion from Celestia and causes her to want to figure out why her sister is suddenly so happy.
Luna lost a long standing bet to Celestia and now she must pay up. Twilight is not thrilled and thinks that giving Celestia a stern lecture will save her marefriend from a terrible fate.
King Sombra has returned, and the mane 6 can't stop him. Instead, Princess Luna is the only one who can stop it, but when a pegasus joins her and they are transfered to a new world with super heros, lets just say things get complcated.
Princess Luna has always been the one to hide her feelings and try to not show signs of weakness but something has been troubling her heart recently. After raising the moon and going out for a flight, she decides to visit Twilight for some advice.