Bargain with the Devil

In Jane Austen's Pride and Prejudice, Fitzwilliam Darcy learns of the debacle involving Elizabeth Bennet's sister several months after he was rejected by Elizabeth, and volunteers to help find her sister, of his own accord.

But what if Miss Elizabeth had requested Mr. Darcy's aid in just a few days after the disastrous proposal at Hunsford, and he was still very angry with her refusal? What if he decided to be ungentlemanly, and demanded a very particular reward from her in exchange for his ...