It started when two people crossed through opposite ends of the portal at the same time.

Rodrick MacBride and Twilight Sparkle are connected through dreams. If one's asleep, they see life through the other's eyes. If both are asleep, they are cast off in a dark realm where they speak with one another.

All the while, the Celestias from both of their worlds have been kidnapped, and they use this communication to their advantage to figure out the mystery behind their disappearance and their super-powered captors.