Milky Holmes decide to go explore the Hakkei Prison Island to find a way to save the academy, but they are captured and imprisoned on arrival. Meanwhile, Henriette and the Gentlemen Thieves have also infiltrated the island in search of a legendary treasure. After hearing about the treasure from an old man, Henriette, along with Milky Holmes, stage a breakout, but end up falling into traps by the prison guard. However, they manage to find their way out and soon find the treasure is a single flower which, when removed, reduces the prison into a pile of sea cucumbers, only to later realise they had set a bunch of criminals into the city.
