The central irony that is present in this tremendous novel is related to freedom and who possesses it and who does not. As the novel progresses, Charles, who apparently seems to have everything in society a man could wish for, comes to realise how actually he is very constrained and trapped by society and its restraints. Ironically, Sarah, the figure who is shunned by society and seems to lack freedom, becomes a symbol of the complete and total freedom that he craves and desires to have himself. Note how freedom is referred to in the following quote:
Under this swarm of waspish self-inquiries he began to feel sorry for himself--a brilliant man trapped, a Byron tamed; and his mind wandered back to Sarah, to visual images, attempts to recollect that face, that mouth, that generous mouth. Undoubtedly it awoke some memory in him, too tenuous, perhaps too general, to trace to any source in his past; but it unsettled him and haunted him, by calling to some hidden self he hardly knew existed. He said it to himself: It is the stupidest thing, but that girl attracts me. It seemed clear to him that it was not Sarah in herself who attracted him--how could she, he was betrothed--but some emotion, some possibility she symbolized. She made him aware of a deprivation. His future had always seemed to him of vast potential; and now suddenly it was a fixed voyage to a known place. She had reminded him of that.
The central irony of this novel therefore relates to the way in which Charles, the novel's protagonist, moves from a position of feeling himself to enjoy freedom only to realise that he suffers from its profound lack. Note how he identifies himself as a "brilliant man trapped; a Byron tamed." This is accompanied by his growing realiation that Sarah, the character who is despised and shunned by society, actually possesses the perfect freedom he so desperately craves. Moving from being happy with his lot, he realises that his lot only represents a "fixed voyage to a known place." Sarah is able to stir up within him an intense desire for the unknown, for the perfect freedom embodied in her life, which is a life lived free from the constraints of society.