Outaishi Denka wa Koukyuu ni Uranaishi wo Goshomou desu

One day, Duchess Forte, a fortune-teller, is falsely accused and threatened by the prince's aides to find the mastermind behind the murderer of the prince and queen from the three princesses of the palace!" If I fail, I will go to prison," She said, and when she began to search the inner palace disguised as a maid, the mysterious Black Knight Alto would help him. Who the hell is he...!?