After attending Princess Twilight Sparkle's Hearth's Warming Eve baby shower, Celestia and Luna are finally overcome with desire to have their own foals. As luck would have it, the previously unknown to them, Hearth's Warming Wishing Star appears to them in the sky above to answer their plight. It casts its magic upon them and then vanishes, telling them they have until sunrise before the spell wears off. There are no new foals in sight, however, Celestia is now a stallion but what does that have to do with anything? Oh...