Miss Bianca back to the Prisoner's Aid Society, the first half of the journey stowing away on a cargo ship and the rest of the way by speedboat (a toy of the Ambassador's son). Miss Bianca plans to bid Bernard one last fond goodbye and return to her home; however, when Bernard volunteers to help Nils at the Black Castle, Miss Bianca impulsively decides to do the same. The three mice hitch a ride on a supply wagon, and travel two weeks across country to the prison, located in the nearly impenetrable ruins of an old castle. They find the castle's only mouse hole in the Head Jailer's office (the only chamber with wooden walls), and set up living quarters. However, expeditions by Bernard and Nils show the mission is nearly hopeless - all the doors in the castle are heavy iron, there are very few places to hide, and they are constantly in danger of Mamelouk, the Head Jailer's gigantic black half-Persian cat. At first, Miss Bianca serves as de Facto chairwoman, but soon begins to take a more active part in the mission when she encounters Mamelouk and discovers her charm and wit both infuriate and fascinate him. She begins to distract Mamelouk by baiting him into conversation and taunting him, both easy tasks as he is incredibly boastful and equally stupid. At one point, she discovers a paper attached by treacle to Mamelouk's fur; this turns out to be a lament written by the Norwegian poet, proving he is still alive. Another day, she is able to get Mamelouk to admit he and all the jailers will be practically comatose on New Year's Day, having eaten and drunk more than their fill at a New Year's Eve party the night before. Bernard and Nils, now able to explore more freely with Mamelouk distracted, discover that the river that runs below the castle, swollen by a sudden storm, has washed away rocks blocking up an old water gate. Mamelouk catches Nils and Bernard as they return to Miss Bianca with the news, but she tricks him into slackening his grip, and they escape. After packing up the living quarters, the mice set out on New Year's Day. They manage to steal the keys from a sleeping/drunk guard, who conveniently had unlocked the cell hall door before he collapsed. They travel past the cells, with Nils calling out in