The Sirens haven't fed on magic in a while, and it's bringing them down.
They discover a new way to harness their magic, but it involves not just two worlds colliding...but three.

Which three worlds? Here's how it works:

Canterlot High School leads to Equestria, and Equestria's very close to two different worlds, that being Canterlot High and one more, Downtown
City--which isn't really it's own world, but where the two intersect. Nevertheless, Downtown City is the home of Littlest Pet Shop, where magic seems to have been used before...

The Sirens send the daycampers of Littlest Pet Shop into Equestria, but how do they get home?
And even then, how did the Sirens send them there, and how do they plan on harnessing the magic?

Sometimes, things aren't always what they seem...