(spoilers)
So this special takes place at the film studio, where director Canter Zoom (an alumni of Camp Everfree who was briefly seen in the background in the final scenes of Legend of Everfree) has given the main 7 full access to witness filming for the new Daring Do movie (much to Rainbow Dash's excitement).
After splitting up to see all the things that interest them, they get back together to see more of the filming, but a series of problems quickly unfolds. A costume goes missing, a set suddenly collapses, and then the most important props (three idols in the form of a staff, a sword, and an arrow) are suddenly missing. With production of the movie now seriously threatened, the girls realize that someone doesn't want the film to be made, so they set out to solve the mystery.
After a series of events (including the girls being mistakenly put in Power Ponies outfits) Twilight eventually manages to figure out all the clues and sets an arrangement that allows them to catch the culprit trying to takes the missing props off the set. It turns out to be Juniper Montage, the director's niece, and her motive is that she so desperately wanted to play the role of Daring Do that she sabotaged production in the hope that she could drive the actress away and thus would have a chance to take on the role (highly flawed logic, in my opinion). Despite being forgiven by her uncle, she ends up being banned from the film lot, and she gives the main 7 an angry stare as she is taken away by security. Finally, as a reward for saving production, the director gives the main 7 minor background roles in the film (much to Rainbow Dash's obvious excitement).
The fact that this special was mostly about solving a mystery, there were arguably quite a few Scooby Doo references, such as chase scenes with music, splitting up to look for clues, and big eater Pinkie Pie with those candy bars and the big tub of pudding. Not to mention, with the way Juniper Montage left, it's very obvious that she's going to do something very big in the next special.
(end spoilers)
