Pride and Prejudice Volume 3, Chapter 10
Mrs. Gardiner's answer to Elizabeth's letter reveals that Darcy was not only the one who found Lydia and Wickham, but also the one who made all the arrangements for their marriage and for paying off Wickham's debts. He didn't want anyone to know of his involvement, though, so he asked Mr. Gardiner to take the credit for it although Mr. Gardiner was uncomfortable taking credit for someone else's good deeds. Darcy claimed that he felt responsible for what happened because he didn't tell anyone in Meryton the truth about Wickham, but Mrs. Gardiner attributes his kindness to his love for Elizabeth. Elizabeth suspects his affection, but believes that despite his feelings, they could never marry for the reasons he'd given her before and now that Wickham is her brother-in-law, marriage must be impossible.
Wickham comes into the garden as Elizabeth is finishing the letter. He asks her about her visit to Pemberley, pumping her to see how much she knows about him. She says enough to let him know that she's not fooled by him anymore in hopes that he'll leave her alone. He drops the subject.