Princess Luna patrols the dreams of everypony as part of her duties as princess of the night… and as her position as Director of the Moonlight Knights, a clandestine organization tasked with protecting Equestria's national security. During these patrols, she discovered many ponies were having nightmares involving a long forgotten race of ponies, the Gorgoneions - a tribe that had serpents instead of hair and the ability to petrify all who met their gaze.

As Princess Luna helped the ponies escape from these nightmares, she heard a sinister, whispered chant, "When the moon is blue. an ancient host shall emerge from the Shadowed Lands like a plague of locusts. Chaos will be sown in their hoofsteps, and all that witness their passing shall be lapidified."

Unsettled by the implications and with the second full moon of the month, the 'blue moon,' scheduled to occur in three days, Princess Luna recruits her top agent, Pinkie Pie, to investigate.