Mrs. Gardiner sends a long reply detailing how Darcy went to London, tracked down Wickham and stopped him from abandoning Lydia and escaping to Europe, and then negotiated a deal with Wickham and presented it to Mr. Gardiner. Darcy would pay and Mr. Gardiner would take all the credit. Mr. Gardiner resisted, but Darcy was firm, arguing that it was his silence about Wickham's character that set all of these problems in motion. Mrs. Gardiner writes that she suspects that Darcy had another motivation, however.
Wickham is ready to abandon Lydia. Darcy realizes that this would wreck the Bennets' reputation and totally prevent any future association he could have with them. As Mrs. Gardiner realizes, Darcy bribes Wickham in order to preserve Elizabeth's reputation, not Lydia's. He then refuses the credit out of pride and respect for Elizabeth.
Before Wickham leaves, Elizabeth encounters him on a walk. She reiterates that she knows his story but, resigned to be his sister-in-law, requests that they not argue about the past.
Elizabeth will be neither fooled by Wickham nor overly prejudiced against him. She shows compassion in accepting Wickham into the family.