The crux comes in a striking scene exactly halfway through the movie when Catherine Dickens makes a surprise visit to Nelly's birthday party, bearing a piece of jewelry that Dickens' had made for Nelly but that was delivered to her by mistake. By ordering his wife to take the gift to its proper recipient, Dickens is announcing his intentions to both women. Catherine, hurt but stoical, urges Nelly to understand that she will have to share Dickens with the public, and may never be sure which he loves best.
Though Dickens soon sends a letter to the Times in which he announces his separation from Catherine and defends the "spotless" honor of the unnamed young woman with whom he has been linked, there is, for reasons the movie doesn't explain, no chance that he will divorce the one in order to marry the other. Thus does Nelly become that which she didn't want to be: a famous man's mistress. They decamp to France, where they have a son who dies in childbirth. On returning to England, they are caught in a horrific train wreck and Dickens emerges trying to make it seem that he was traveling alone.