When Louisa and Tom discuss their futures, and Tom says that he has already anticipated a means by which to gain the upper hand over Bounderby, which is an instance of foreshadowing:
“Oh,” said Tom, laughing, “I don’t mind that. I shall know very well how to manage and smoothe old Bounderby!”
Their shadows were defined upon the wall, but those of the high presses in the room were all blended together on the wall and on the ceiling, as if the brother and sister were overhung by a dark cavern. Or, a fanciful imagination—if such treason could have been there—might have made it out to be the shadow of their subject, and of its lowering association with their future.
This scene foreshadows Tom’s manipulation of Louisa into marriage with Bounderby for his own personal gain.
Though they are inside, the siblings appear to have a “dark cavern” hanging over them. The narrator reveals that an imaginative viewer would see this as the “shadow of their subject” and its “lowering” influence on their future. The darkness in the room echoes the secrecy and dark self-centeredness of Tom’s intentions, which threaten to “lower” his relationship with Louisa and degrade them both morally. The shadows appear to “blend” on the wall and ceiling, as if to suggest the ill-fated blending of families.
This foreshadowing prepares the reader for Tom’s ultimate betrayal of his sister. This passage lays the groundwork for his actions later on, rendering them more believable than they would be otherwise. This foreshadowing also signals to the reader that despite her curiosity and goodness, Louisa’s future will likely not be a happy one, creating a sense of dread and suspense.