Zephyr and Gloamwing, a male pegasus, and a female bat pegasus respectively, were the most inseparable of friends in the brief time they knew each other as foals. Many years later, both have become seasoned members of Celestia and Luna's royal guard, and finally get the chance to see each other once again when an archaeological expedition set to the frozen north pairs both their squads together to accompany it. As they catch up and are just discovering that their friendship, still going strong after so long, may be evolving into something more, a terrifying threat arises in the perilous frozen wastes as a malevolent, mechanical being begins to ruthlessly pursue the group.