Night One

"Why is she standing out there? What does she want?"

Night Two

"There's something off about her...."

Night Three

"That's not Fluttershy..."

Sooner or later, everyone finds their way to Roseluck's flower stall. And then they leave.

Part of Twilight's Library
Now available as an audio book
And also in Russian apparently

After the changelings' failed invasion of Canterlot, Twilight tries to soothe some of Ponyville's rampant paranoia by casting a spell to prove there are no imposters hiding in the town. But her spell leaves her in an alien body, facing a mob of angry ponies who just don't believe her when she says she is Twilight Sparkle.

Or, at least, she was Twilight Sparkle, anyway...

Featured on Equestria Daily, 2/17/13
Cover art is by the awesome and amazing Conicer