For a three-act plot analysis, put on your screenwriter’s hat. Moviemakers know the formula well: at the end of Act One, the main character is drawn in completely to a conflict. During Act Two, she is farthest away from her goals. At the end of Act Three, the story is resolved.
Act I
We meet some of the folks who inhabit Dawson's Landing, including the stars of our show: Pudd'nhead Wilson, Roxy, and Tom. Then Roxy takes our breath away with the stunt she pulls in making the switcheroo of Tom and Chambers.
Act II
After getting himself into a ton of gambling debt, Tom starts robbing houses in the neighborhood to get money to pay off his creditors. When that doesn't pan out, he decides to rob his own uncle. But, uh, that doesn't go exactly as planned either and he ends up killing him with a stolen knife. The knife's owner, Luigi, is charged with murder (and his twin brother Angelo is named an accessory to the crime). Pudd'nhead takes on their defense, but the case against them looks seriously bleak.
Act III
A-ha! Pudd'nhead makes a discovery and proves to the court that the twins didn't commit the murder after all and that Tom is the true scoundrel who did. Plus, he reveals that the identities of Tom and Chambers were switched when they were kids, making Tom a slave. The twins are freed, Tom is put in jail and then sold into slavery, and Pudd'nhead will never again be called, well, Pudd'nhead.