The third out of six movie sequels to the Princess Principal TV series. 

While the funeral of the assassinated Prince Edward, who was the first in line to succeed the throne, is being held, the nobles of the Kingdom of Albion discuss topics such as whether the second-in-line Princess Mary or the third-in-line Duke of Arkham, Prince Richard, will succeed the throne, and how the Duke of Normandy will act.
 
The Duke of Arkham asks Princess if she will side with him or the Duke of Normandy. While wishing to change the world so that all people are equal, Princess is shaken by the Duke of Arkham, who is the mastermind behind Edward's assassination. Meanwhile, Ange and Dorothy are given a mission to infiltrate as Mary's maids and investigate the state of the royal family by the Commonwealth's control. Mary is crushed and exhausted due to the pressure of becoming first in line to the throne. As chaos surrounds the succession to the throne, the Duke of Arkham's plot finally begins to unfold.
 
The darkness writhing in the Kingdom of Albion begins to swallow up Team White Pigeon.
 
(Source: Official site, translated)

Princess Principal: Crown Handler - Chapter 3