looking for a story

I am looking for a story where the baby son of Richard Fitzwilliam and Anne de Bourgh is taken from France to England to the Darcys who have
to protect the baby from the Earl of Matlock and Lady Catherine de Bourgh.The lady who brings baby to the Darcys is the wife of an officer
in Richards regiment.Hoping someone knows the name of the story.
Cheers Bernie