When the Cutie Mark Crusaders dig up an ancient magical artifact, they unleash a spell on the town that allows everypony to see a "lie meter" floating above each other's heads. While attempting to solve the mystery, Twilight Sparkle has to analyze the tenuous balance between friendship and honesty. She doesn't like what she finds.
You would think that a story about a magic lie detection field permeating Ponyville would feature Applejack prominently, and be about honesty and stuff like that. But in fact this was a surprisingly deep story focused on Twilight, and ultimately illustrating why it is that Twilight is the element (and eventual Princess) of Friendship. She really is good at the friendship thing, it turns out. Quite a nice twist.
A very entertaining fanfic that puts an interesting spin on all the main characters. It derives humor from its lie detector plot device in pretty much every way I could have thought of, and more.