When Arthur Clennam returns to England after many years abroad, his curiosity is piqued by the presence in his mother's house of a young seamstress, Amy Dorrit. The cold and forbidding Mrs Clennam isn't usually given to charity, so why has she made an exception in taking on Amy? Is she making reparations for a past wrongdoing? Does it have anything to do with Arthur's father's dying words and the pocket watch with its mysterious inscription, 'do not forget'?

Arthur befriends Amy Dorrit and involves himself in her family's affairs. If, as he suspects, his family have something to do with their ruin, the least he can do is pay off her brother's debt and give him the chance to start again. Arthur himself is planning to start again with a new job, and perhaps a renewed love for childhood sweetheart Flora Casby.

Flintwinch taunts Arthur's mother about the mystery at the heart of the House of Clennam, while Amy discovers that 'a gentleman' has paid off her brother's debts, and Arthur is invited to Twickenham to renew his acquaintance with the lovely Pet Meagles.

Amy receives a proposal of marriage which throws her into confusion, Arthur is taken on as a partner in Daniel Doyce's engineering works, and the French villain Rigaud arrives in London.

Amy accompanies her sister Fanny to meet Mrs Merdle, queen bee of London society. Meanwhile, Rigaud comes into possession of the Clennam papers, and Chivery the turnkey asks Arthur to put in a word for young John with Amy.

Pancks recruits John Chivery to help him solve the mystery that connects the Dorrit family with the House of Clennam, while Arthur proposes to Pet Meagles. Elsewhere, Tattycoram runs away from Twickenham, and Amy resigns herself to a life without the man she loves.

Rigaud introduces himself to the House of Clennam, while Arthur is best man at Pet's marriage to Henry Gowan. Pancks concludes his investigation into the Dorrit family's long incarceration in the Marshalsea Debtors' Prison, and Arthur and Amy break momentous news to Mr Dorrit.

Mr Dorrit is released from the Marshalsea after more than twenty years, and takes his family abroad to reinvent themselves as members of society. Miss Wade commissions Rigaud to spy on Pet and Henry Gowan, and he takes the chance to follow the Dorrits abroad and find out what connects them to the House of Clennam.

The Dorrits arrive in Venice, and Fanny renews an old acquaintance with Edmund Sparkler and his redoubtable mother Mrs Merdle. Meanwhile, Amy makes a friend in Pet Gowan, united through their mutual affection for Arthur, and Rigaud scents a deeper connection between the Dorrits and the House of Clennam.

Romance is in the air as Mrs General starts her campaign to woo Mr Dorrit, and Fanny turns the full beam of her attention on Sparkler. Meanwhile, an unwelcome reminder of the old days comes to haunt Mr Dorrit in Venice.

Mr Dorrit leaves Amy behind in Venice as he returns to London with newlyweds Fanny and Sparkler, but the high life is not all he had hoped it would be. Meanwhile, Arthur invests Doyce and Clennam's capital in Merdle's Bank, and Flora investigates the disappearance of Rigaud.

Mr Dorrit returns to Venice, a broken man, after a visit to London revives unwelcome memories. Arthur warns his mother that she may be in danger from Rigaud. And Amy and Arthur meet again.

Mr Merdle's death and the collapse of Merdle's Bank sends shockwaves through London as thousands face financial ruin. Arthur returns to the Marshalsea a prisoner, Amy goes back to her birthplace to look after him as he lies gravely ill, and Rigaud returns to play out his blackmail in the Clennam house.