Queen Chrysalis (a changeling who feeds off of the emotions of ponies, more obviously love) begins to set a plot in motion to feed from her "love" interest. Not only does she informs Princess Celestia of a threat to Canterlot disguised as a guard, but she also manages to infiltrate the living quarters of Princess Cadence. Cadence, who was one night brushing her mane, had looked in her mirror to find a shadow-like figure standing behind her...

And as the clock struck twelve midnight, Cadence was gone and Queen Chrysalis took her place.

The wedding day came and her victory was close at hand, that is until an angry Twilight Sparkle interrupted the ceremony with the real Princess Cadence standing beside her. Chrysalis then resorts to plan b; breaking the magic shield surrounding Canterlot that Shining (who is currently trapped in a mind control spell) put up. Princess Celestia then opts to protect her subjects from the usurper.