It's been inching towards one whole year since Twilight Sparkle made her first foray into an entirely different universe inhabited by an entirely alien race... and inching towards one whole year since she'd started her relationship with a member of said alien race she'd befriended during her travels. She and the human being known as Ty had been together long enough that they'd been able to see beyond the basic differences between them and their respective worlds and cultures in the name of their affections for one another, all the while mulling over how to reveal the true, unorthodox nature of their courtship to the public.
However, when a sudden issue arises within Twilight concerning her biology; an issue neither of the two had done more than touch on, she contemplates how to inform her special someone without alarming him. Unfortunately, a foreign threat comes to Equestria with malevolent plans (with perfectly wrong timing), forcing the two and the others into action...
{Sequel to Twi and Ty's Topsy-Turvy Tours and its subsequent Spin-Offs}