In another dimension, Equestria is modern. Luna has nothing to do with her time, no friends either, so she bothers Celestia to no end. Eventually, fed up with her complaints of boredom, and intrusion on her work, she sends her out to go find some friends and a hobby. Perhaps that was a bad idea. Oh dear Celestia, what have you done? You sent your 20-year-old equivalent of a sister into Equestria to find something to do, and she returns with more immature, 20-year-old ponies, ready to mess up more than Celestia's peace and quiet.