Chizuko Mikamo is a young girl living with her aunt and uncle after her parents died. She behaves coldly toward them, despite their efforts to make her happy, because she knows that they are trying to slowly poison her so that they can take her inheritance for themselves. Because of her intelligence and knowledge gained from reading detective novels, she works to avoid eating the food her aunt prepares, but it is impossible to avoid all together and she still takes in enough to cause her to collapse. Her butler is revealed to actually be the world-famous thief Twenty Faces, who was there to steal Chizuko's rightful inheritance, a family heirloom gem known as the Anastasia Ruby. When he realizes just what Chizuko's been going through, however, he asks her if she wants to come with him and his band on their travels around the world. She agrees and Twenty Faces takes her back with him to join his gang, who affectionately shorten her name to Chiko. Two years pass and Chiko is now a strong thief, having learned the tricks of the trade from Twenty Faces and the members of his band. Now, with Twenty Faces and the rest of the band as her family, she has found a home at last.
After living with the band for two years, Chiko becomes a skilled thief and thinks of Twenty Faces as her father. But a sudden train accident caused by Tiger, Twenty Faces' strongest enemy, kills most of the band and seems to have killed Twenty Faces himself. By chance a detective who works for her aunt finds her and, after being "rescued" two years after Twenty Faces "kidnapped" her, Chiko is forced to return to her aunt's house, where she becomes depressed and refuses to eat or talk because of the shock of Twenty Faces' death. But when a mysterious detective appears and she learns that there is a possibility that he may still be alive somewhere, Chiko becomes more lively and works, with the help of a few new friends, to find him by following the clues that he seems to have left behind, beginning with something that is rightfully hers and had been left in his care: the Anastasia Ruby. Now, Chiko must dodge her aunt's attempts to murder her and unravel the mysteries Twenty Faces left for her to solve, or so it seems. There are many steps in her long journey, some of which awaken painful memories and others that lead her to discover more about the past of the man behind Twenty Faces and herself.