Following his father's death John Harmon returns to London to claim his inheritance, but he finds he is eligible only if he marries Bella Wilfur. To observe her character he assumes another identity and secures work with his father's foreman, Mr Boffin, who is also Bella's guardian.
Disguise and concealment play an important role in the novel and individual identity is examined within the wider setting of London life: in the 1860s the city was aflame with spiralling financial speculation while thousands of homeless scratched a living from the detritus of the more fortunate-indeed John Harmon's father has amassed his wealth by recycling waste.