Princess Principal/Recap/S1/E02 Case 1 Dancy Conspiracy

Quoting from Wikipedia: "In the past, Ange begins attending Queen's Mayfair school as a transfer student. Ange links up with fellow agent Dorothy; their primary mission is to secretly replace the Princess with Ange. That night, Ange and Dorothy attend a ball at the school and are given an impromptu mission to keep a key away from the Duke of Normandy. Dorothy approaches Morgan, who is in possession of the key, but is turned away by his bodyguards. Ange then goes over to the Princess to befriend her, while "accidentally" spilling a "drink" on her dress. While Princess waits for a new dress, Ange impersonates her to get the key from Morgan. However, Princess is already aware that Ange and Dorothy are spies, and offers to work with them if they help her become Queen of the Kingdom. Ange signals to her handlers to ring a nearby church bell if they accept Princess's terms. The Duke of Normandy realizes the key has been taken from Morgan and orders a search of everyone at the party. As he approaches Ange, the bell tower chimes, distracting the Duke and sealing Ange's bargain with Princess. Princess uses the diversion to secretly take the key from Ange and then excuses herself from the ballroom. The next day, Ange and Princess meet on the roof of the school, revealing that Ange was the one who tipped Princess off to her identity as a spy. It is also revealed that Ange's real name is Charlotte and Princess' real name is Ange, and that both girls had known each other ten years ago."


 * Conspicuous CG: Although it maintains a look of traditional cel animation quite well, the illusion fails during the traveling shot when the Princess's party returns to the ball.
 * Country Mouse: The character Ange effects for the ball where she meets Princess is so Country Mouse that it should have been a red flag that something was wrong. Only the fact that she only speaks to the Princess in-character -- and that the Princess knew something was up and was playing along -- kept her from being thrown out as a gate-crasher far out of her social stratum.