The night after meeting the Lammles, Mr. Boffin kisses his wife and heads out on the town. He goes to meet with Mr. Venus and the two of them head to Mr. Wegg's house (which is actually Boffin's house).
At the house, Wegg decides that the time has come to spring his trap. He tells Boffin all about the will he found. You know, the will that leaves all of Old Man Harmon's money to the government and nothing to Mr. Boffin.
Mr. Boffin asks to see the will, so Wegg leads him to Venus' shop and holds his arms behind his back while Venus shows him the piece of paper. Boffin has no choice but to admit defeat. He is Wegg's slave now.