Changelings have lived in Equestria for a long time, and have survived by staying hidden and keeping their existence a secret.

Meeting Driftwood of Portside forced Princess Twilight Sparkle to begin recognizing her stance on changelings, and how that stance informs and influences her decisions as the Princess of Friendship. When she returns from Hoofington, she discovers that there are changelings secretly living in Ponyville, and that they've been living there almost as long as she has.

More than deciding how she should react to some of her closest friends keeping secrets from her for fear of how she may react, she must confront herself and her beliefs. The presence of changelings in Ponyville will challenge not only her as a pony, but as a Princess as well, and her decisions and actions will reach far beyond the borders of Ponyville when the time comes.