Twilight Sparkle knows Rainbow Dash; the pegasus is her wife, after all. But ever since Twilight crashed in the Everfree forest on her way to Zecora's hut, something has been wrong with Rainbow. The mare is off, in a way Twilight can't quite explain. She's off in such a way that Twilight knows it's not the real Rainbow Dash. It's an imposter.

All she has to do is prove it, and get her real wife back.