I switched your question to the proper group which is
Pride and Prejudice.
Assuming you are talking about the elopement of Wickham and Lydia, this is what happened. Lydia is basically a very thoughtless creature who fantasizes about being married, and to marry an officer in uniform. Wickham was an immoral, irresponsible and equally worthless individual who took advantage of her looseness, and eloped with her as part of his being an adventurer. In the end, Mr. Gardiner, the person in charge of Lydia at the time she was staying there, finally found them, and they were married off thanks to money that was actually given by Darcy, to secure a dowry and try and save her reputation.