Wickham seduces the younger Bennet daughter, Lydia,  and runs away with her away from Brighton as- where it is mentioned multiple times in the novel beforehand that the military encampment near Hertfordshire is, and where Lydia had spent time visiting. 

'"I have just had a letter from Jane, with such dreadful news. It cannot be concealed from any one. My youngest sister has left all her friends—has eloped; has thrown herself into the power of—of Mr. Wickham. They are gone off together from Brighton. You know him too well to doubt the rest. She has no money, no connections, nothing that can tempt him to—she is lost for ever.'"