Convulted codicil subplot

I never really understood what the Rigaud/Blandois character was doing in this book (or in the most recent TV adaption). At long last we get to the bit where the hold he has over Mrs Clennam is explained, and we find out what is was she was told not to forget about. It all seems convoluted and absurd. Arthur's father had got a young girl up the duff. The baby was Arthur. Mrs Clennam forced the young woman to give up the child to her. Then I think (I am not sure) Flintwinch got his twin brother to lock her up in an asylum where she died. Arthur Clennam's father, or it might have been his great uncle, wrote something to the effect that a lot of money be left to Arthur's real mother, or if not her, Arthur's mother's patron's daughter, of if not her, Arthur's mother's patron's brother's daughter. Arthur's real mother's patron turned out to be Frederick Dorritt. So the money should have gone to Amy Dorrit, or possibly her and her sister. Arthur's real mother was training to be a singer at Frederick Dorritt's theatre company in the years before he was financially ruined. Mrs Clennam should have burnt the piece of the paper when she could, but she didn't, then Flintwinch for some reason passed it on to his twin brother, and Blandois got it off him. 0/10 for plausibility.

I am annoyed I spelt convoluted incorrectly.

Someone else blogged about codicil.
Apparently, this was changed a bit in the most recent TV adaption to make it a bit more understandable.

I think I would have changed it so that Frederick Dorrit had loaned Arthur's mother some money, maybe for some business venture, or maybe it was a crucial bridging loan. She passed the money onto Arthur's father, who was her common law husband. Then Mrs Clennam found out about her relationship with her husband and the smelly stuff hit the forced convection device. Arthur's real mother went mad and died and Frederick never got his money back. She was never officially married to Arthur's father, so what could Frederick do? Frederick was not the most forceful of men, so he might not even have chased it up very vigorously. Maybe Frederick did not have a record of the money he had lent, at least not one that was legally enforcible. Maybe on the Clennam side there was better paperwork, but in the turmoil of Arthur and his father leaving for China, it got forgot about until it was rediscovered later. It could be Arthur's real mother had written a will (when she was in sound mind) leaving whatever she had to her son, but I suppose when someone dies their creditors should be paid out of the estate before the heirs. The money would not be owing to Amy Dorrit directly, but Mrs Clennam would later feel she was helping the family by employing her. It could be Frederick Dorrit left whatever he had to Amy, although Mrs Clennam would not have known about that.