chunk: The fraudulent dealings (similar to a Ponzi scheme) of Edmund Sparkler's stepfather, Mr. Merdle, end with his suicide and the collapse of his bank business, and with it the savings of both the Dorrits and Arthur Clennam, who is now himself imprisoned in the Marshalsea, where he becomes ill and is nursed back to health by Amy. The French villain Rigaud, now in London, discovers that Mrs. Clennam has been hiding the fact that Arthur is not her real son, and tries to blackmail her. Arthur's biological mother was a beautiful young singer with whom his father had gone through some sort of non-marital ceremony, before being pressured by his wealthy uncle to marry the present Mrs. Clennam. The latter insisted on bringing up little Arthur and denying his mother the right to see him. Arthur's real mother died of grief at being separated from Arthur and his father; but Mr. Clennam's wealthy uncle, stung by remorse, had left a bequest to Arthur's biological mother and to "the youngest daughter