In Chapter IV of Volume III of this novel, Lizzie reads the letters that have been sent to her by her sister Jane. However, she is greatly upset to read of one particular piece of news that will change the rest of the novel significantly. This is of course the news that her youngest sister, Lydia, has eloped with one of the officers in Colonel Forster's regiment in Bournemouth. The officer turns out to be Wickham, as the following quote from this letter explains:
An express came at twelve last night, just as we were all gone to bed, from Colonel Forster, to inform us that she was gone off to Scotland with one of his officers; to own the truth, with Wickham!
This of course is ironic in a number of ways. Lizzie has just learnt the truth about Wickham and his habit of preying upon young defenceless women, as he tried to do with Georgiana Darcy. Also, Wickham is a man who Darcy now has a hatred of, and so it is highly unlikely that a man such as Darcy will have any further dealings with her, as is suggested before this point.