When Jane receives an invitation from the Bingley girls to dine at Netherfield, Mrs. Bennet seizes the opportunity to put a cunning plan into effect. She instructs Jane to travel to Netherfield on horseback. Mrs. Bennet figures that, as it will be raining when Jane arrives, she'll be invited to spend the night at Netherfield, thus giving her an opportunity to get to know the dashing Mr. Bingley a little better.
Mrs. Bennet's plan works, but only up to a certain point. Jane is indeed invited to spend the night at Netherfield, but that's only because she's wet through from the rain and has developed a nasty fever. When the Bennets receive word of Jane's illness, Elizabeth immediately sets off for Netherfield, tramping through the sodden fields, as there are no horses available. As one can imagine, once Lizzie arrives, her clothes are all spotted with mud, much to the horror of the Bingley sisters. However, Lizzie is invited inside and spends all her time keeping vigil by the stricken Jane's bedside. As Jane doesn't want Lizzie to leave her side, Caroline Bingley invites her to spend the night at Netherfield.