I'm thinking of starting with a classic "King hires young hero to rescue his kidnapped daughter" story, which ends with the protagonist about to slay the antagonist. As he's about to save the day, the princess releases herself and saves the bad guy. The hero asks if it's some sort of mind control potion, to which the princess replies "I concocted the whole plan. Lord [whatever his name is] works for me. With my father's greatest hero out of the way, we'll conquer the kingdom and run things my way!" You may be wondering why the princess wouldn't just wait for her father to die, but that's to be revealed in the story proper. But have you seen ever seen the abductee turning out to be the mastermind before?
There have been countless crimes where the kidnapping turned out to have been faked by the supposed victim, and TVTropes has an extensive list of works that have used this as a plot twist for fiction: http://tvtropes.org/pmwiki/pmwiki.php/Main/FakedKidnapping Sounds like there's a very solid market for this type of storyline. Go for it
After checking the list, I can't see any examples of this in Fantasy, though I may have missed them. Looks like there's a niche! Thanks for the tip.
The first Hoodwinked movie comes to mind. It's not the same set-up precisely, but the character that turns out to be the criminal mastermind towards the end deliberately pretended to be saddened and adversely affected by what turns out to have been his own evil doings. Snow White and the Huntsman also has similarities, where a beautiful and powerful witch disguises herself as poor and imprisons herself to be found by the king of a rival kingdom, ending up being found by, marrying and killing him all on one day and then running the entire country into the dirt in a matter of days.
