What crisis happens involving Lydia in Pride and Prejudice?

The conflict was solved after the letter which Darcy wrote to Elizabeth. It was only after reading the letter that Elizabeth started to realise her misjudgement and started to reflect and changed her opinion of Darcy. Elizabeth was able to forget about her initial prejudice of Darcy and see things from another point of view. Darcy's willingness to ditch his pride also contributed to the improvement in their relationship.