After his night with the prostitute, Charles has decided that he’ll go through with his marriage to Ernestina, though he never really doubted he would. The prostitute Sarah has stood in for Sarah Woodruff, and so ended his relationship with her. Even so, Charles wishes her letter had shown some clearer emotions. But sending her address is certainly a rebellion. Clearly he must ignore it. However, his night with the prostitute has reminded him of some of Sarah’s more remarkable qualities. As he travels towards Lyme, Charles thinks that sending Sarah to an asylum would have been a mistake. She comes to him in images, though he tells himself he’s simply concerned for her welfare.
Charles had such a viscerally negative reaction to his own defiance of conventional morality that it helped him decide to return to the straight and narrow Victorian path of marriage. Besides, he thinks he’s had symbolic closure, even though he acknowledges that the prostitute Sarah only made him think about how amazing Sarah Woodruff is. It’s pretty clear that Charles is lying to himself about being over Sarah, as he continues to think about her and wonder what her attitude is towards him.
When the train gets to Exeter, Sam asks whether they’re staying the night there, and Charles says they’ll continue on. Sam was sure they were going to stay, but when Charles saw his face he decided they must go on. As they’re leaving the city, Charles feels that this one decision has fixed his future. He’s done the right thing, but it seems to show a despicable willingness to accept fate. He knows he’ll eventually go into commerce to make Ernestina happy. It’s drizzling, and Charles would usually let Sam sit inside the carriage with him, but he feels like he needs to relish the last of his solitude. He thinks of Sarah as a symbol of all of his lost freedoms. He knows he’s just a fossil caught in the drift of history. Finally he falls asleep.
Sam actually unconsciously influences the course of Charles’s life here, although it could be said that Charles’s own fear of judgment is what forces him to make the decision he does. This decision spells the end of Charles’s sense of his own free will, and he once again thinks of himself in terms of evolution—no longer one of the fittest, but a fossil that will have no impact on the world. However, the narrator will soon reveal that none of this actually happens. The rest of the novel really does hinge on this one decision of whether to stop in Exeter.