In "Lyddie", what happened with Mrs. Marsden, Lyddie, and Brigid?How did Lyddie handle Mr. Marsden and how did she protect Brigid?

In Chapters 20 - 22, Lyddie notices that Brigid is missing one day as they leave from work.  She goes back to find her, and discovers Mr. Marsden making inappropriate advances towards Brigid in the weaving room where he has detained her.  Lyddie snatches the fire bucket and jams it over Mr. Marsden's head, then grabs Brigid's hand and makes a quick escape.  Brigid doesn't show up at work the next day, having been informed that she need not come.

Lyddie is later called before the agent who administers the affairs of the mill.  She is accused of being immoral and a troublemaker, and is dismissed.  Although she herself does not know what she will do now, Lyddie is more concerned about Brigid, whom she knows is desperately in need of a job to help feed her imooverished family.  She devises an ingenious plan to get back at Mr. Marsden and to protect Brigid, giving him a letter warning that if Brigid is dismissed or harrassed in any way, a second letter will be given to his wife, telling her exactly what happened between him and Brigid in the weaving room.  Mrs. Marsden is known as a formidable woman, and Mr. Marsden is intimidated by her.  Lyddie can leave the mill confident in the knowledge that Brigid will be safe and her job secure.