Most good stories start with a fundamental list of ingredients: the initial situation, conflict, complication, climax, suspense, denouement, and conclusion. Great writers sometimes shake up the recipe and add some spice.
Initial Situation
Everybody is in chains, everybody pants for freedom.
Nearly every character starts out somehow enslaved. Dorrit is literally in prison and Amy Dorrit is mired in drudgery trying to take care of him. Arthur is stuck as a partner in Clennam & Co. with his horrible mother. Tattycoram is trapped as a second banana with the Meagleses, while Pet is stuck in their doting care.
Conflict
New relationships are formed, old relationships are threatened.
When Arthur and Amy grow close, Dorrit is jealous of his daughter's slightly diverted attention and tries to suck her back into the morass by suggesting she hang out with the turnkey's son instead. Meanwhile, Pet turns from the loving affection of her parents to the cynicism and jerkishness of Henry Gowan. It's a nice change of pace for her. Finally, Tattycoram runs away and joins Miss Wade's circus of tears and anger.
Complication
The Dorrits are rich now, so it's out with the old and in with continental Europe.
Dorrit basically spits on everyone he used to know and takes his family to the continent to get to know high society. Amy and Arthur are parted, and Dorrit threatens to marry Amy off like her sister. Pet and Gowan go to the continent, too, where the high society that knows Gowan frowns on Pet as a status-seeking climber.
Climax
Merdle's enterprises implode! Also, Blandois is blackmailing Mrs. Clennam!
Everyone loses all their money, and Arthur is forced to go to jail for his debts. The financial upheaval is shocking and a great equalizer, as Arthur is forced to see what life was like for Amy. Also, something sinister is going on at Mrs. Clennam's, where a deep dark secret is threatening to come to light – exposed by Blandois, who wants a lot of money for his silence.
Suspense
Will Blandois be found? What's going on with the Blandois/Mrs. Clennam mystery?
Blandois disappears and makes it look like Mrs. Clennam hired a hitman. There is a multi-person search for him, as Pancks, Cavalletto, and Meagles try to find him all over Europe. On top of that is the mystery of what he knows about the Clennams in the first place. It's a bit of a nailbiter, as Arthur falls ill in jail and no one knows whether Blandois will ever be found.
Denouement
Secrets are uncovered, then buried forever.
Oh, there he is! Cavalletto finds Blandois, who immediately resumes his blackmailing tactics. We finally learn the awful truth about Mrs. Clennam: her stealing Arthur from his real mother and her suppression of a will that would have left a lot of money to Amy. As soon as the secret comes out, the Clennam house literally falls down, killing Blandois. Mrs. Clennam becomes catatonic, and Flintwinch escapes to Amsterdam. So there is no one except Amy left who knows the secret.
Conclusion
Semi-happy ending for all.
Amy and Arthur get married, and she decides to eventually tell him the truth about his family. Other than that, the vain get their comeuppances with uncomfortable lives full of grasping and striving, and everyone who was nice to Amy gets a pretty content existence.